Plasma chemistry derived formation rock evaluation for pulse power drilling

ABSTRACT

During pulse power drilling, the formation rock type is determined by analyzing organic and inorganic chemical reaction products. Plasma pulses interact with the solid rock of the formation to shift downhole chemical reactions. The formation type may act as a catalyst or an inhibitor to enhance or degrade reactions. The concentration of organic and inorganic chemical reaction products is determined by analyzing the reactions occurring at the drill bit. From the concentrations, the formation rock type is determined.

TECHNICAL FIELD

The disclosure generally relates to pulse power drilling operations, andin particular, to plasma chemistry derived formation rock evaluation forpulse power drilling.

BACKGROUND

Mud logging during drilling of a wellbore can provide information aboutgeological formations and fluid. Such information can be correlated topetrophysical properties and depths within the formation during wellboredrilling based on testing and measurement of drilling mud returned tothe surface. Drilling mud (also referred to as mud) is the fluid thatcan be pumped down the drill string in order to lubricate the bottomhole assembly and drill string, to suppress fluid or gas ingress intothe bore hole and maintain pore pressure, and also to remove cuttingsfrom the well as it circulates to the surface.

When wellbores are drilled in a geological formation, information aboutthe formation layers and fluids—such as lithology, porosity,permeability, petrochemical type, petrochemical concentration, etc.—canbe determined based on the chemical composition of the mud, cuttings,and dissolved gasses returned to the surface. In traditional mudlogging, a record of the characteristics determined from the drillingmud can be kept as a function of drilling depth in order to correlaterock, fluid, and gas characteristics to layers and reservoirs at depthsin the formation.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the disclosure may be better understood by referencing theaccompanying drawings.

FIG. 1 depicts an example pulse power drilling system for mud logging,according to one or more embodiments.

FIG. 2A depicts electrodes of a pulse power drill string at the bottomof a wellbore prior to emission of a pulse into the formation, accordingto one or more embodiments.

FIG. 2B depicts the electrodes of a pulse power drill string of FIG. 2Aduring emission of a pulse into the formation, according to one or moreembodiments.

FIG. 2C depicts electrodes of a pulse power drill string at the bottomof a wellbore after emission of a pulse into the formation, according toone or more embodiments.

FIGS. 3A-3B depict a flowchart of example operations for pulse power mudlogging, according to one or more embodiments.

FIG. 4A depicts an example line graph of the reaction kinetics andreaction path of an example plasma-mediated chemical reaction, accordingto one or more embodiments.

FIG. 4B depicts example reactants and products as well as examplereaction pathways, according to one or more embodiments.

FIG. 5A depicts the geometric approximation for a plasma arc, accordingto one or more embodiments.

FIG. 5B depicts the geometric approximation for a plasma spark,according to one or more embodiments.

FIG. 6 depicts a flowchart of example operations for determining rocktype based on plasma chemistry, according to one or more embodiments.

FIG. 7 depicts an example mass spectrometry graph, according to one ormore embodiments.

FIG. 8 depicts an example computer, according to one or moreembodiments.

DESCRIPTION

The description that follows includes example systems, methods,techniques, and program flows that embody aspects of the disclosure.However, it is understood that this disclosure may be practiced withoutthese specific details. For instance, this disclosure refers to pulseddirect current (DC) plasma in illustrative examples. Aspects of thisdisclosure can be also applied to sustained or alternating current (AC)plasmas. Additionally, while analysis may be described in reference tobeing performed at the surface of the borehole, example embodiments caninclude at least a partial analysis downhole. For example, some or allof the analysis can be performed in a downhole tool of the drill string.In other instances, well-known instruction instances, protocols,structures, and techniques have not been shown in detail in order not toobfuscate the description.

Overview

Formation evaluation is the analysis of subsurface formationcharacteristics, such as lithology, porosity, permeability, andsaturation. Conventional techniques for formation evaluationcharacterize the subsurface environment before or during drillingthrough mud logging, wireline logging, coring, drill stem testing,measurement while drilling (MWD), or logging while drilling (LWD). Whilethere are several different downhole methods for characterizing aformation, data density is often lacking. Additionally, these methodstend to produce bulk measurements that are not representative of theentire subsurface formation. By analyzing events at the bit using pulseplasma drilling, the rock type of the formation being drilled can bemore accurately determined.

In pulse plasma drilling, a pulse plasma drill bit drills a wellboreusing electric pulses that include short duration, periodic,high-voltage pulses that are discharged through the formation. Suchdischarges can create high internal pressure to break or fracture therock from the inside (breaking from tension). Such pulse plasma drillingcan involve generating a plasma, a high energy fluid, in the drillingfluid or rock downhole which functions as a high-energy discharge.Plasma can be a highly conductive, ionized gas containing free electronsand positive ions (from which the electrons have been disassociated). Inthe high temperature and high-pressure environment downhole, thecreation of a plasma involves injecting large amounts of energy into thesubsurface formation. Ideally, the energy would be injected entirelyinto the subsurface formation as mechanical crushing force. However, aportion of the energy may also be absorbed by the drilling fluid and/orthe formation. For example, a portion of the energy may be absorbed bythe drilling fluid when the drill string is not in contact with a bottomof the borehole when the energy is discharged from the electrodes of thedrill string due to borehole irregularities, or due to bottom holeassembly geometry. The conductivity of the formation is independent ofthe formational fluid in the pore spaces of the formation. Theindependent conductivity allows for energy losses due to absorption bythe formation to be distinguished from other losses.

Some embodiments can perform evaluation of the rock of the subsurfaceformation at or near the drill bit based on analysis of the chemistrychanges of the downhole fluid that has interacted with the pulses ofplasma emitted as part of the pulse power drilling. For example, anattribute of the subsurface formation (such as type of rock) can bedetermined based on this plasma chemistry analysis. Thus, the changes inchemistry of the downhole fluid can be correlated to an attribute of thesubsurface formation that is at or near the drill bit.

For example, in response to the energy being injected into thesubsurface formation, ionic bonds within the rock of the formation canbe broken and solid rock from the formation and/or formation fluid canbe vaporized. The energy output from the electrodes of the drill stringcan also create chemical reactions between the species downhole. Thesechemical reactions can generate chemically complex molecules whichshould be accounted for in mud logging because these complex moleculesare not constituents of either the formation fluid or the drilling mud.The loss of energy to the formation can change the energy available forchemical reactions independent of the fluids. The reduction in energyfor plasma-based chemistry can shift possible chemical reactions. Thiscan be quantified through analysis of the resultant products. The energyshift can come in two forms. Either the possible formational compoundsthat can catalyze the reaction will change, or the aqueous or organicliquid phase reactions will shift. The application of the formationconductivity at the bit with possible chemical reactions allows theformation type to be determined from the formational and non-formationalfluids produced at the surface by correlating the concentration oforganic and inorganic chemical species to plasma generation parameters.Organic chemical species are chemical species or chemical compounds thatcan contain carbon and hydrogen, specifically carbon bonded to hydrogen,such as hydrocarbons. Inorganic chemical species are chemical species orcompounds that do not contain carbon bonded to hydrogen. Examples ofinorganic chemical species include salts, metals, substances made fromsingle elements, and any other compounds that do not contain carbonbonded to hydrogen.

Example System

FIG. 1 illustrates a schematic diagram of a pulse power drilling system(a system 100), according to one or more embodiments. The system 100 asillustrated in FIG. 1 includes a derrick 101 positioned on a platform102 that is located above a surface 103 and covering a wellhead 104. Thewellhead 104 includes a borehole 110 that extends from the surface 103into one or more layers of a subterranean formation 113. The borehole110 may include borehole walls 111 that extend substantially verticallyfrom surface 103 and parallel to one another, forming, and at leastpartially enclosing, the space within the borehole that extends fromsurface 103 to a borehole bottom surface 112. Although shown as havingsubstantially a vertical orientation in FIG. 1, embodiments of theborehole 110 are not limited to vertically orientated boreholes, and mayinclude at least some portion(s) of the borehole that extend at an anglerelative to vertical, including in some embodiments portions of theborehole that may extend horizontally in a direction parallel to thesurface 103.

The system 100 includes a drill string 120 that may be positioned overand extending downward into the borehole 110. The drill string 120 maybe supported at an upper portion by a hoist 105 suspended from derrick101 that allows the drill string 120 to be controllable lowered into andraised to different depths within the borehole 110, and/or inserted intoand completely withdrawn from the borehole 110. The drill string 120 maybe coupled to a hoist 105 through a kelly 106 and may extend through arotary table 107 positioned adjacent to and/or extending though anopening in a platform 102. The rotary table 107 may be configured tomaintain the position of the drill string 120 relative to the platform102 as the drill string 120 is extended through the opening in theplatform 102 and into the borehole 110. The drill string 120 maycomprise a plurality of sections of drill pipe 121 coupling a lower ordistal end of the drill string 120 to a bottom hole assembly (BHA) 122.The BHA 122 includes a pulse power drilling (PPD) assembly 126 havingelectrodes of the drill bit 123 and a pulse-generating circuit 135.

Referring again to FIG. 1, a drilling fluid 130, such as drilling mud,may be initially sourced from a fluid pit 140, which may be referred toas a “mud pit.” Although, depicted below the surface 103, the mud pitcan be equipment located on the surface 103 as well. A pump 141 may beused to suction the drilling fluid 130 from the fluid pit 140 through afluid conduit 150, and provide a pressurized flow or circulation of thedrilling fluid 130 through a fluid conduit 151 to the upper portion ofthe drill string 120, as illustratively represented by the solid linearrows included within the fluid conduits 150 and 151. The drillingfluid 130 may then proceed through the sections of the drill pipe 121that make up portions of the drill string 120, providing a fluidpassageway for the drilling fluid 130 to flow from the upper portion ofthe drill string 120 to the BHA 122 positioned within the drill string120.

The flow of the drilling fluid 130 is directed through the BHA 122 andexpelled from one or more ports included in the electrodes of the drillbit 123. The drilling fluid 131, as illustratively represented in FIG. 1by dashed-line arrows, that has been expelled from ports on, or through,the electrodes of the drill bit 123 helps to remove formation materialthat has been broken up by the electrical energy generated at theelectrodes of the drill bit 123 in a direction away from the electrodesof the drill bit 123 and away from a borehole bottom surface 112.

In addition to carrying away broken up formation material, the flow of adrilling fluid 131 may also represent drilling fluid that has beenexposed to or that has otherwise interacted with the electrical energybeing applied by the electrodes of the drill bit 123 to the boreholebottom surface 112 and/or to the drilling fluid in the vicinity of theelectrodes of the drill bit 123. The drilling fluid 131 is illustratedas broken-line arrows to represent drilling fluid that may have one ormore chemical properties and/or one or more physical properties of thedrilling fluid that have been altered due to the interaction of thedrilling fluid 131 with the electric energy provided by the electrodesof the drill bit 123. The flow of the drilling fluid 131 continues toflow back upward toward the surface 103 through the annulus 114 of theborehole 110. The annulus 114 are formed by the space between theborehole walls 111 and the outer surfaces of the drill string 120. Thedrilling fluid 130 flowing into the drill string 120 from the mud pitcan be referred to as “influent,” and the drilling fluid 131 flowingfrom the electrodes of the drill bit 123 back the fluid pit 140 as“effluent”. In one or more embodiments, this drilling fluid 130, theinfluent or inward flow, and the drilling fluid 131, the effluent orupward/outward flow, are part of a continuous circulation of drillingfluid.

As the upward flow of the drilling fluid 131 reaches the surface 103,the flow may be directed into fluid conduit 152, which directs the flowof returning drilling fluid 131 to a fluid reconditioning system 142.The fluid recondition system 142 may comprise any number of devices,such as shakers, screens, and/or wash stations, which are configured toprocess the drilling fluid 131, for example to remove and/or recovercuttings from the drilling fluid 131 being processed. In one or moreembodiments, the fluid reconditioning system 142 can include one or moreof desalters, de-sanders, and de-gassing apparatus. The fluidreconditioning system 142 may also process the drilling fluid 131 torefine or alter other properties of the drilling fluid 131, for exampleto remove dissolved or suspended gasses present in the drilling fluid131. The fluid reconditioning system 142 may also be configured to addchemicals, such as high dielectric constant muds or clays, conductivenanoparticle suspensions, weighting agents, etc., to the drilling fluid131 to alter or reinforce various performance properties of the drillingfluid 131 before the drilling fluid 131 is ultimatelyreturned/recirculated to the borehole 110. Upon completion of theprocessing of the drilling fluid 131 passing through the fluidreconditioning system 142, the drilling fluid 131 may be returned to thefluid pit 140 through a fluid conduit 153. The drilling fluid 131returned to the fluid pit 140 may then become available forrecirculation to the borehole 110 as described above.

An extraction system 144 is fluidly coupled to the circulation of thedrilling fluid 131 via a fluid conduit 157 running from the fluidreconditioning system 142 to extract an effluent sample of the drillingfluid 131 that has exited the borehole 110 via the fluid conduit 152.The extraction system 144 is optionally also coupled to the fluidconduit 151 via the fluid conduit 158 to extract an influent sample ofthe drilling fluid 130 prior to its entering into the drill string 120.

In one or more embodiments, the extraction system 144 includes one ormore gas extractors to extract a gas sample from the drilling fluid 131,one or more sampling apparatus to sample or extract the liquids portionof the fluid, or both. The extraction system 144 can sample gas orliquids directly from the fluid reconditioning system 142 or (althoughnot shown) from another point in the flow of drilling fluid 131 from theborehole 110 or the flow of the drilling fluid 130 into the drill string120.

In addition to the returning drilling fluid being directed to the fluidreconditioning system 142 as described above, in various embodiments ofthe system 100 a portion of the returning drilling fluid is directed toa sample analysis system (the analysis system 160). The extractionsystem 144 directs drilling fluid (e.g. effluent drilling fluid 131)extracted or sampled from the fluid recondition system 142 to theanalysis system via fluid conduit 159. In one or more embodiments, theextraction system 144 extracts or samples influent drilling fluid 131,e.g., from fluid conduit 151 as shown or, although not shown, from oneor more other points in the influent side of the system, e.g. from fluidconduit 150 or from the fluid pit 140.

The analysis system 160 may include an instrumentation 161 and acomputer 162. An example of the computer 162 is depicted in FIG. 1,which is further described below. The instrumentation 161 may compriseone or more devices configured to measure and/or analyze one or morechemical and/or physical properties of the drilling fluid provided tothe analysis system 160. Illustrative and non-limiting examples of thedevices that may be included as part of the instrumentation 161 includeone or more gas chromatograph (GC) (e.g., one or more of a gaschromatography-isotope ratio mass spectrometer (GC-IRMS), gaschromatography-infrared isotope ratio analyzer (GC-IR2), dual gaschromatograph with a flame ionization detector (FID), or the like) andone or more mass spectrometer (e.g., one or more of an isotope ratiomass spectrometer (IRMS), magnetic sector mass spectrometer,Time-of-Flight mass spectrometer (TOF-MS), triple quadrupole massspectrometer (TQMS), tandem mass spectrometer (MS/MS), thermalionization-mass spectrometer (TIMS), inductively coupled plasma-massspectrometer (ICP-MS), Spark Source mass spectrometer (SSMS), or thelike). In one or more embodiments, instrumentation 161 can furtherinclude one or more of a liquid chromatograph, a laser spectrometer, amultivariate optical computing device (e.g. one or more integratedoptical element), a nuclear magnetic resonance (NMR) measurement device,a cavity ring-down spectrometer, an electromechanical gas detector, acatalytic gas detector, an infrared gas detector, a cutting analysistool or system for further analysis of the gas, liquid, and/or solids.In one or more embodiment, the instrumentation 161 also can include oneor more temperature sensors for measuring the temperature of theeffluent and/or influent samples, and can include one or more pressuresensors to measure the pressure of the effluent and/or influent samples.These sensors or others sensors can also be distributed at differentpoints along the fluid circulation path, such as in the extractionsystem 144, the pump 141, the BHA 122, the drill string 120, the annulus114, along any of the fluid conduits 150-159, and/or at another point inthe fluid circulation path.

The instrumentation 161 may provide one or more measurements ordetermined outputs to the computer 162 that can be used as inputs forfurther analysis, learning, calculation, determination, display, or thelike. The fluid samples received by, or continuous measurements obtainedby, the analysis system 160, e.g. as inputs to the computer 162, may becorrelated with time, depth, and/or other information related to theinteraction of the fluid sample with electrical energy emanating fromthe electrodes of the drill bit 123. For example, a particular sample ofdrilling fluid may be correlated to a specific time and/or a depth wheredrilling fluid sample was when the fluid interacted with electricalenergy emanating from the electrodes of the drill bit 123. In someembodiments, this correlation is based, at least in part, on themeasured rates for flow of the drilling fluid down through the drillstring 120 and back up through the annulus 114 over time to determinewhen the sample of drilling fluid being analyzed interacted with theelectrical energy provided by the electrodes of the drill bit 123.

The computer 162, in some embodiments, is integral with one or more ofthe devices included the instrumentation 161, and/or may be separatecomputer device(s) that may be communicatively coupled to the devicesincluded in the instrumentation 161. In other examples, the computer 162may be computing devices, such as personal computers, laptop computers,smartphones, or other devices that allow a user, such as a fieldtechnician or an engineer, to enter, observe, and otherwise interactwith various software applications providing data reports and controlinputs for the measurements and analysis being performed on the drillingfluid by the analysis system 160.

In various embodiments, although not shown, the computer 162 may becommunicatively linked with other devices, such as the BHA 122, the pump141, the extraction system 144, and/or the fluid reconditioning system142. The communication provided between the computer 162 and otherdevice within the system 100 may be configured to allow the computer 162to adjust operating parameters, such as but not limited to adjusting theflow rates of drilling fluid provided to the drill string 120, controlover the positioning of the drill string 120 with the borehole 110, andcontrol over the operating parameters associated with the electricalgeneration and application of electrical power being performed by thebottom hole assembly 122.

Communications from the computer 162 may also be used to gatherinformation provided by the fluid reconditioning system 142, and/or toprovide feedback to the fluid reconditioning system 142 to control theprocesses being performed on the returning drilling fluid by the fluidreconditioning system 142.

The analysis system 160 and the extraction system 144 (from theextracted samples from the influent 130 and the effluent 131) can outputone or more compositions of the drilling fluid, one or more compositionsof the formation fluid, and/or one or more isotope ratios. For example,the extracted sample from the influent 130 can be used as a baseline todetermine the contribution of the formation fluid and/or a downholereaction at the drill bit to the composition of the effluent.

The analysis system 160 may determine various parameters related to theformation 113, and/or various parameters related to the operation of thepulse power drilling assembly, based on measurements and/or analysisperformed to determine various chemical and/or physical propertiespresent in the drilling fluid that has been exposed to or that hasotherwise interacted/reacted with the electrical energy provided by theelectrodes of the drill bit 123. Further, various operating parameters,such as electrical parameters, associated with the discharge of theelectrical energy from the electrodes of the drill bit 123 withinborehole 110, may be measured and analyzed to derive data and makedeterminations about various parameters associated with the formation113, parameters associated with properties of the drilling fluid,parameters associated with the operating parameters of the BHA 122,and/or parameters associated with the operating parameters of the PPDassembly 126.

In various embodiments, the system 100 may include the analysis system160 having a communication link, illustratively represented by alightning bolt 164, configured to provide communications between theanalysis system 160 and one or more remote computer systems 163. Theremote computer systems 163 may be configured to provide any of the datafunctions associated with and/or the analysis function described abovethat may be associated with the drilling fluid as provided by theanalysis system 160. In various embodiments, the remote computer systems163 may including storage devices, such as data storage disks,configured to store the data being generated by the analysis beingperformed by the analysis system 160. In various embodiments, the remotecomputer system 163 may include display devices, such as computermonitors, that allow users at remote location, i.e., locations away fromthe location where the system 100 is physically located, to visually seeand interact with the visual representations of the data being providedby the analysis system 160. In various examples, control inputs, asdescribed above, may be provided via user input provided to the remotecomputer systems 163 and communicated to the analysis system 160 for thepurpose of controlling one or more of the operating parametersassociated with system 100.

In some embodiments of the system 100, the BHA 122 includes a samplingtool 124. The sampling tool 124 may be located within the housing of theBHA 122. The sampling tool 124 may be coupled to the annulus 114 throughthe port 125, wherein the port 125 provides a fluid communicationpassageway between the annulus 114 and the sampling tool 124. In variousembodiments, the port 125 may be used to collect a sample of drillingfluid, such as the drilling fluid illustratively represented bydashed-line arrows 131. The sample of collected drilling fluid may beprovided to the instrumentation 161, where one or more measurementsand/or further analysis of the drilling fluid may be performed by thesampling tool. Measurements made, e.g., from one or more pressure ortemperature sensors and/or a multivariate optical computing device,and/or data collected from the analysis of the samples of drilling fluidcollected through the port 125 may be communicated through acommunication link, e.g., via wired (like a wireline or wired pipe) orwireless telemetry (like mud pulse, acoustic, or electromagnetictelemetry) to the surface, and optionally to the analysis system 160. Inthe alternative or in parallel with the above, the sample of drillingfluid collected through the port 125 may be contained, for examplebottled, and then transported back to the surface with the BHA 122. Anysamples of drilling fluid collected via the port 125 may be data stampedwith information indicating the time, depth, and/or other informationassociated with the collection of the fluid sample.

FIGS. 2A-2C depict electrodes of a pulse power drill string at thebottom of a wellbore at three different points in time relative to theemission of a pulse into the formation, according to one or moreembodiments. FIG. 2A depicts electrodes of a pulse power drill string atthe bottom of a wellbore prior to emission of a pulse into theformation, according to some embodiments. In this example, a drill bitincludes electrodes depicted as an anode 202 and a cathode 204. Theanode 202 and the cathode 204 can be examples of the electrodes withinthe drill bit 123 of the drill string 120 of FIG. 1.

In pulse power drilling, the anode 202 and the cathode 204 (when notperforming off-bottom analysis) can rest along a bottom 250 of thewellbore in contact with a formation 208. The formation 208 includes anumber of pore spaces 214 having formation fluid. One or more of theelectrodes can be charged by portions of the drill string as describedabove. This charging can induce charge carriers at the electrodeformation interface—either electrons or holes which are theoreticalcharge carriers representing the absence of electrons. For simplicity,only electrons 206 are shown.

The dielectric between the anode and cathode can be comprised of theformation rock or stone, the formation fluid in the pores of the rockstrata, and the drilling fluid pumped downhole. The dielectric, beforethe plasma is applied, can be approximated as a resistor 212 in parallel(or alternatively in series) with a capacitor 210, where the dielectricstrength can be a function of porosity, permeability, formation type,formation fluid composition, and drilling fluid composition.

FIG. 2B depicts the electrodes of a pulse power drill string of FIG. 2Aduring emission of a pulse into the formation, according to someembodiments. As shown in FIG. 2B, a plasma discharge into the formation208 can result in vaporization of the fluid in the pore spaces 214,which causes expansion of the liquid in the pores as it is converted toa high-pressure vapor or gas, and leads to destruction of the rock.Formations without pore spaces, or with small, impermeable pore space,are also susceptible to pulse power drilling. In such dry formations,the plasma discharge occurs through the rock itself, which then suffersfrom dielectric breakdown, creating fissures and fault lines along thecurrent path. Vaporization of fluid is a faster pulse power drillingmethod, but both mechanisms can be active in the same rock at the sametime.

At the pressure and temperature of a wellbore, the ideal gas law is nota good approximate of the volume of a gas. The gas volume forhydrocarbons is modeled using the Wilson model, or anotherthermodynamically complex model or approximation. The volume of gas(such as H₂, CO₂, etc.) generated downhole—but not the volume of vaporgenerated (such as steam)—can be calculated from the volume of gasevolved at the surface. The volume of gas detected at the surface can beconverted to a molar amount via the ideal gas law (see Equation 1below).PV=nRT  (1)Where P is pressure, Vis volume, n is the number of moles of the gas, Ris the ideal or universal gas law constant and T is temperature inKelvin. At high temperatures and pressures downhole, the ideal gas lawapproximation can be inaccurate and gas volume is calculated usingWilson's equation for a multi-component fluid (see Equation 2 below) ora similar equation.

$\begin{matrix}{{\ln\left\lbrack \gamma_{k} \right\rbrack} = {1 - {\ln\left\lbrack {\sum\limits_{j = 1}^{n}\left( {x_{j}A_{kj}} \right)} \right\rbrack} - {\sum\limits_{i = 1}^{n}\left\lbrack \frac{x_{i}A_{ik}}{\sum_{j = 1}^{n}\left( {x_{i}A_{ij}} \right)} \right\rbrack}}} & (2)\end{matrix}$Wilson's model determines the liquid phase activity coefficient γ forcomponent k as a function of the molar fraction x_(n) of each of ncomponents, where A_(ij), A_(ji) are the Wilson coefficients for thebinary pair of components i and j. The liquid phase activity coefficientγ is related to the partial pressure of each compound in the fluid viaRaoult's law (Equation 3) or a similar approximation.p _(k) =x _(k)γ_(k) p _(k) ^(σ)  (3)In Raoult's law, p_(k) ^(σ) is the saturation pressure or vapor pressureof the undiluted component (i.e. of each component in its pure form).

Current flows from the anode 202 to the cathode 204, which correspondsto a flow of the electrons 206 from the cathode 204 to the anode 202.The electrons 206 are injected from the cathode 204 into the dielectricunder the influence of the electric field generated between the anode202 and the cathode 204. The electric field can be approximated for aparallel plate capacitor as given by Equation 4 below:

$\begin{matrix}{E = \frac{\Delta V}{d}} & (4)\end{matrix}$Where E is the electric field (in Volts (V) per meter or another unit)for a parallel plate capacitor approximation for electrodes separated bya distance d and at a voltage difference of ΔV. The electric fieldbetween the anode 202 and the cathode 204 is not uniform if theformation is not microscopically uniform, which is true for anyformation strata with fluid filled pores. The average electric field canbe approximated as shown in Equation 5:

$\begin{matrix}{\overset{\_}{E} \sim \frac{\Delta V}{d}} & (5)\end{matrix}$Where Ē is the average electric field in the dielectric between theelectrodes, ΔV is the voltage drop from anode to cathode (or between theelectrodes, generally) and d is the separation distance between theelectrodes.

The electrons 206 accelerate in the electric field in the dielectricuntil they experience a collision with particle. The collision ofcharged particles in a plasma can generate an avalanche multiplicationcurrent, as described by Townsend (and further explained in reference toFIGS. 5A-5B). Similarly charged particles repel each other, but neutraland opposite polarity particles experience collisions at appreciablerates. The electron 206 collides with water molecule 218 leading to thegeneration of an additional electron. This collision would be governedby the hydroxide ion chemical formation shown in Equation 6 below:e ⁻+H₂O↔½H₂+HO⁻+2e ⁻  (6)where e⁻ represents electrons and HO⁻ represents hydroxide ions. Anotherreaction pathway generates hydroxyl radicals but no additional electronsas shown in Equation 7:e ⁻+H₂O↔½H₂+HO.+e ⁻  (7)Where HO. represents a neutral hydroxyl radical, and where free radicalsor radicals are electrically neutral molecules with at least oneunpaired electron and can be very reactive. In this way, the plasmagenerates high energy particle collisions that produce chemicalreactions downhole.

A portion of the electric current travels not between the cathode andanode, but out into the formation as plasma sparking. The portion of theplasma power that generates a plasma spark 216 or sparking does not leadto appreciable current transfer between the anode and cathode—althoughcurrent may flow to ground or into the formation. Sparks of plasmatypically have higher plasma temperatures than arcs of plasma, as willbe discussed in more detail below in reference to FIGS. 5A-5B, whichaffects the types of products generated and their reaction rates. Plasmasparks also vaporize fluid, breakdown rock, and contribute to drilling.Plasma sparks can be undesirable because they unevenly form at oneelectrode, instead of dissipating power equally between both anode andcathode. However, plasma sparks may be useful in directionally modifyingdrilling such as when turning the wellbore is required.

FIG. 2C depicts electrodes of a pulse power drill string at the bottomof a wellbore after emission of a pulse into the formation, according tosome embodiments. The vaporization of the formation fluid generatesexpansive gases. As the plasma is quenched, the gasses are dissolvedinto the high-temperature and high-pressure drilling fluid. Theformation solids (rocks or particulates), having been broken intosmaller pieces by the plasma, are carried away as cuttings by thedrilling fluid. The destruction of the solid matrix frees fluid 220formerly trapped in pore spaces within the rock. However, the fluid 220from the regions where plasma was generated is no longer formation fluidbut rather plasma reaction products. This too travels to the surfacedissolved in the drilling fluid to be analyzed and categorized.

Example Operations

Example operations are now described. The following description ofexample operations include Subsections A-B. Subsection A includes adescription of example pulse power mud logging operations (FIGS. 3A-3Band 4-5). Subsection B includes a description of an example of derivingformation rock type based on plasma chemistry (FIG. 6-8).

A. Example Pulse Power Mud Logging Operations

FIGS. 3A-3B depict a flowchart of example operations for pulse power mudlogging, according to one or more embodiments. A flowchart 300 of FIG.3A and a flowchart 350 of FIG. 3B includes operations described as beingperformed by the pulse power drilling and mud logging system forconsistency with the earlier description. However, program code naming,organization, and deployment can vary due to arbitrary programmerchoice, programming language(s), platform, etc. The flowchart 300includes blocks 302, and the flowchart 350 includes blocks 310, 312, and330 depicted with broken lines. Such blocks represent examples ofoperations that can be optionally performed. This depiction of theblocks of the flowchart 300 and the flowchart 350 should not beinterpreted as requiring operations in the blocks depicted with solidlines, as one or more other operations in the solid blocks can beoptional also. Operations of the flowchart 300 start at block 302, whileoperations of the flowchart 350 continue at blocks 310, 314, and 316from block 309 of the flowchart 300.

FIGS. 3A-3B include operations related to plasma parameters, mudlogging, and drilling optimization for an example pulse power drillingsystem. Pulse power mud logging includes several methods fordetermination of formation fluid and generation of mud logging recordsbased on both downhole drilling measurements and on surface fluidcharacterization. The relationship between the chemical composition ofdrilling mud returned to the surface (including cuttings and solids,dissolved gasses, and liquid hydrocarbons) and the formation fluidsentering the wellbore downhole can be complicated by the plasma pulsescreated while drilling and the destructive reactions thereby engendered.By iteratively or sequentially solving a number of groups of equationsand balances, the total degrees of freedom of the system can be reducedso that the problem is solvable—that is the formation fluidconcentration can be determined or back calculated. The determinationsteps are shown here in a particular order, which is illustrative only,and it should be noted that each balance, set of equations, ordetermination can be applied in any order, including stepwise oriteratively.

At block 302, drilling mud to be pumped downhole is analyzed withformational fluid analyzers. For example, with reference to FIG. 1, theinstrumentation 161 can perform this analysis as the mud enters thewellbore to be pumped downhole. The concentration of hydrocarbon speciesin the drilling mud can measured using analyzers and detectors similarto those used to analyze the chemical composition of the drilling mudreturned to the surface in block 308 (as further described below).Optionally, the same analyzers can be used to determine the compositionof the drilling mud returned to the surface and the drilling mudentering the wellbore. Because the drilling mud circulates through thewellbore, chemical reactions downhole cause drift in the mud's chemicalcomposition. Measuring the drilling mud's chemical composition as themud enters the wellbore allows the mud logging system to account for theinitial concentration of hydrocarbons and water (as shown in Equation 8)and determine the change in concentration for each iteration through thewellbore precisely.ΔP=[P]_(product)=[P]_(exiting wellbore)−[P]_(entering wellbore)  (8)Where P is an example product molecule or species, [P] is aconcentration of the example product and can be normalized for flowrate, rate (as of time), or volumetrically, and the concentration of Pcan change as a function of time of as a function of the total volume ofdrilling mud. ΔP represents the total change in product in the drillingfluid due to one cycle through the wellbore and corresponding exposureto plasma.

In some embodiments, if the drilling mud is not analyzed as it entersthe wellbore, the drilling mud composition is assumed from the chemicalcomposition of the drilling mud as it reaches the surface, which isdetermined at blocks 308 and 309, minus the concentration of gasses,which are removed from the drilling fluid before it enters the mud pitor another storage unit (as further described below in reference toblock 316).

At block 304, temperature and, optionally, pressure downhole aremeasured. For example, with reference to FIG. 1, the computer 162 canperform this operation. The temperature of the drilling fluid can affectthe reaction rate constants and plasma parameters, such as breakdownvoltage, dielectric constant, etc. The mud logging system can correlatethe downhole temperature to drilling mud analyzed at the surface byadjusting for drilling mud pumping speed and drilling speed.

At block 305, a determination is made of whether an electric pulse isemitted from the drill bit. As described above, the electrodes in thedrill bit periodically emit an electric pulse to drill the borehole. Forexample, with reference to FIG. 1, the computer 162 can determine whenthe electric pulse is emitted. If there is no electric pulse emitted,operations of the flowchart 300 remain at block 304. Optionally, flowcan continue to block 308 in the absence of a detected pulse and performmud logging calculations based on possible plasma reaction products indrilling mud that may result from previous reactions. The drilling mudcirculation time causes a temporal mismatch between when the pulse isdetected and when the products are detected and analyzed at block 308.Otherwise, operations of the flowchart 300 continue at block 306.

At block 306, the plasma energy is determined based on electrodecurrent(s) and voltage(s). For example, with reference to FIG. 1, thecomputer 162 can make this determination. The plasma energy can bedetermined based on anode and cathode current and voltage of the drillbit. Plasma power calculations can assume that power added to the systemis approximately equal to the plasma power, or can account for powerlost to the formation, heat of vaporization, etc.

In a closed-loop system where electrons are neither created nordestroyed, the current flowing through the system can be determinedbased on current measured at the anode (the anode current) and at thecathode (the cathode current) as given by Kirchhoff's current law.Kirchhoff's current law does not apply in a plasma, as the accelerationof electrons in the electric field of the plasma can cause Townsendavalanche multiplication, as will be discussed later. Electrons andpositive ions can be created in the plasma. However, the electrons andpositive ions can recombine when the plasma generation ends to formneutral molecules which are the reaction products. Once initiated, theplasma itself can be considered a conductor of infinite conductivity orzero resistance.

When the anode and cathode currents are equal and the plasma isquenched, no current flows into the formation or away to ground. If theanode and cathode currents are unequal, the difference can representcurrent lost to the formation or current created by the electrons andions generated by the plasma. Current lost to the formation can beapproximated as current lost to ground where the formation functions asa grounding electron sink. The relationship between anode, cathode, andformation current is then given by Equation 9 below:I _(anode) =I _(cathode) +I _(formation) +I _(plasma)  (9)Where I_(anode) represents the current flowing out of the anode,I_(cathode) represents the current flowing into the cathode, andI_(plasma) represents any additional current generated by the plasma.I_(formation) represents any current lost to the formation or otherwiseaway from the anode or cathode, or another electrode. For pulse powerdrilling in a wellbore, the formation current is approximately theground current as shown in Equation 10, below:I _(formation) ≈I _(ground)  (10)Where I_(ground) is the current lost to or gain from ground, which isapproximately the formation or earth acting as an electron sink.I_(formation) and I_(ground) may or may not be measurable.

Plasma can form in the combination of drilling mud, rock or formation,and formation fluid when the applied voltage is above the dielectricbreakdown voltage of that combination, for the downhole temperature andpressure. At voltages above breakdown, electrons separate frommolecules, generating positive ions. The electrons have much smallermass than the positive ions and accelerate in the electric field towardsthe anode. In a low-pressure plasma, the mean free path of the electronscan be long, and the electrons may experience significant acceleration.Very fast electrons can generate additional electrons through theTownsend avalanche multiplication when they collide with positive ionsor neutral molecules on their way to the anode. In a high-pressureplasma where free electrons can be drawn from ground, such as found whendrilling in a formation, the mean free path of the electron can be soshort that avalanche electron multiplication is negligible. In eithercase, the increase in current generated by the plasma is encompassed bythe term I_(plasma).

The value of the Townsend current is given by Equations 11-12, below:

$\begin{matrix}{I = {I_{0}e^{\alpha_{n}d}}} & (11)\end{matrix}$ $\begin{matrix}{I = {{I_{0}\frac{\left( {\alpha_{n} - \alpha_{p}} \right){{Exp}\left\lbrack {\left( {\alpha_{n} - \alpha_{p}} \right)d} \right\rbrack}}{\alpha_{n} - {\alpha_{p}{{Exp}\left\lbrack {\left( {\alpha_{n} - \alpha_{p}} \right)d} \right\rbrack}}}} \cong {I_{0}\frac{{Exp}\left\lbrack {\alpha_{n}d} \right\rbrack}{1 - {\frac{\alpha_{p}}{\alpha_{n}}{{Exp}\left\lbrack {\alpha_{n}d} \right\rbrack}}}}}} & (12)\end{matrix}$I₀ represents current generated at the cathode surface (which can beapproximated as I₀=I_(cathode)), α_(n) is the first Townsend ionizationcoefficient, α_(p) is the secondary ionization Townsend coefficient, andd is the distance between the anode and cathode of a parallel platecapacitive discharge. α_(n) represents the number of particle pairsgenerated by a negatively charged particle (anion or electron) per unitlength, where such a negative particle is moving from cathode to anode.α_(p) represents the number of charged particle pairs generated per unitlength by a cation, during its collisions while moving from anode tocathode. Equation 11 considers only electrons traveling at speedssufficient to cause ionization collisions (i.e. a non-thermal plasma),while Equation 12 also considers positive ion (i.e. cation) travelingfast enough to impart ionization energy to neutral particles (i.e. athermal plasma).

For a downhole plasma where d is known, the plasma current can bedetermined or estimated based on an exponential fit to the anode andcathode currents. The exponential portion of the increase in currentduring the lifetime of the plasma results from the avalanchemultiplication in the plasma. Current lost to the formation or groundshould exhibit only minimal capacitive or inductive charging (i.e.current that depend exponentially on time) and is predominantlyresistive in nature and therefore distinguishable from the plasmacurrent.

A plasma arc can be defined as a plasma generated between the cathodeand anode along with a significant transfer of current. A plasma sparkcan be defined as a non-directional or isotropic plasma without adirectional current transfer. Plasma arcs between the cathode and anodeand through the dielectric that can include the formation fluid,formation, and drilling mud, but can also arc between either of theelectrodes and the formation or subsections of the formation. Plasmaarcs can be detectable from their effect on the cathode and anodecurrents. Plasma sparks, where electrons are not accelerated appreciablybetween the cathode and anode, can be detectable via their drawn down ofvoltage (or power) from the anode and cathode. Plasma arc and plasmasparks can have fundamentally different plasma temperatures andgeometries, which can lead to different high-energy transition statesand chemical reactions, which will be discussed in more detail below inreference to FIGS. 5A-5B. For pulse power generation, the determinationof a ratio between a plasma arc and plasma sparking can be estimated viaelectrical measurements and further or iteratively refined based onconcentration of chemical products and determination of reaction ratesfrom surface stoichiometric analysis.

The power added to the system can be determined by the current flowingthrough and the voltage drop over the system. If the cathode and theformation are at 0 volts (V) or ground, then the total power added tothe system is given by the anode current multiplied by the anodevoltage, as given by Equation 13 below:P=I _(anode) V _(anode)  (13)Where P represents power in this instance (in units of Watts orequivalent), I_(anode) is the current flow at the anode electrode, andV_(anode) is the electric potential (or voltage) of the anode. Equation14 describes the general relationship between power, current, andvoltage for electric systems.P=IV  (14)Where power P is equal to current I multiplied by voltage V.

If the cathode is not also a ground source or if information about thecurrent and voltage at the cathode is known, then the power added intothe system is given by the approximation of Equation 15, below.P=I _(anode) V _(anode) −I _(cathode) V _(cathode)  (15)Where I_(cathode) is the current flow at the cathode electrode andV_(cathode) is the electric potential of the cathode (which is the sameas its voltage).

The plasma power, i.e. the power consumed to generate the plasma, can beassumed to account for the power input into the system. The plasma powerapproximation can be iteratively updated as a function of time. For asystem where only the current at one electrode or the total power addedto the system is known, the plasma power can be correlated to reactionrates, activation energies, and product concentrations instead ofdirectly calculated. Pulse power discharges of similar power can beassumed to have similar properties, including spark vs. arc ratio,reaction rates, etc.

The power balance represents an instantaneous energy balance, wherepower is energy per unit time. The total energy balance of the systemalso provides information about the plasma power. For a plasma pulse ofknown duration, energy balance equations can be substituted for powerbalance equations. In this case, the total energy of formation of theproducts relates to the power or energy of the plasma. If products andproduct concentrations of the chemical reactions are known, a totalchemical energy balance can be determined based on the enthalpy offormation of the product species and the temperature and pressure atwhich the reactions occur.

In the total energy balance, the total energy added to the fluid by theplasma also accounts for changes in temperature and pressure within thefluid. The plasma can result in vaporized fluids, such as those withinpores in the formation rock, entering the drilling fluid as gasses. Theenergy absorbed by the physical state change can be calculated from theheat of vaporization and the concentration of the gaseous products.Other fluids experience temperature changes, where the energy occupiedby heating such fluids can be calculated from the specific heat ofcapacity multiplied by the temperature change. As fluid in the wellboreheat and/or vaporize, pressure changes can occur. The increase inpressure can account for additional energy in the system stored asincreased enthalpy.

In either case, the power or energy of a given plasma pulse iscorrelated to the products of such a reaction which reach the surface ata time delayed from the reaction. Traditional mud logging correlatesdrilling mud chemical constituents to the depth at which they enteredthe borehole. Pulse plasma mud logging additionally correlates drillingmud chemical constituents to a specific reaction time, current, andvoltage in order to back calculate formation fluid properties. The lagbetween pulse power reaction and drilling mud arrival at the surface isdetermined based on drilling rate, circulation rate, and drill depth.

For a DC plasma, current will vary with time, even during the plasmapulse itself. Before the plasma is generated, the current is low and theresistivity between dielectric between the anode and cathode (which canbe modeled as the drilling fluid resistivity, formation rockresistivity, and formation fluid resistivity in parallel) is high. Thevoltage between the anode and cathode builds as the cathode is chargeduntil the voltage applied over the dielectric is greater than thedielectric's breakdown voltage and a plasma is generated.

The resistivity of the plasma is low, and it can be modeled as aconductor of zero resistivity between the anode and cathode. If thereare available free electrons in the system, an approximation applicablewhen electrons can be drawn from ground or stripped from water moleculesin the drilling fluid, the current generated by the plasma can beestimated by the Townsend discharge equations (Equations 11-12, above)or determined via Kirchhoff's law from the other known currents.

A plasma is overall electrically neutral—the electrons generated by theavalanche cascade reactions are compensated by free electrons absorbedfrom ground or generated by ionization. The number of positive ions(cations) and electrons (where the contribution of anions can beapproximated as n_(a)≈0) are approximately equal. The degree or fractionof ionization for a plasma is given by Equation 16, below:

$\begin{matrix}{f_{i} = \frac{n_{e}}{\left( {n_{e} + n_{0}} \right)}} & (16)\end{matrix}$Where n_(e) is the number of electrons, n₀ is the number of neutralatoms or molecules, and f_(i) is the ionization fraction.

Each particle in the plasma has a kinetic energy. Because there are somany electrons, ions, and atoms or molecules, the kinetic energy is ovenexpressed as an energy distribution or particle temperature. The plasmatemperature of electrons is given in Equation 17, below for aMaxwell-Boltzmann distribution.

$\begin{matrix}{T_{e} = {\frac{2}{3}\frac{\left\langle E \right\rangle}{k_{B}}}} & (17)\end{matrix}$Where T_(e) is the electron temperature,

E

is the average plasma energy, and k_(B) is the Boltzmann constant. TheMaxwell-Boltzmann probability distribution describes a distribution ofparticle kinetic energy or speeds at thermodynamic equilibrium and iscommonly used in statistical mechanics to approximate particlevelocities and interactions as a function of temperature. Electrontemperature is a fundamental measure of the energy of the electrons in aplasma and is used to calculate other plasma properties, such ascollision rate, mean free path, etc., and is often given in units ofKelvin (K) or electron Volts (eV).

Plasmas are classified as either thermal, where anions, cations, andelectrons have similar kinetic energy (i.e. are in thermal equilibrium)and non-thermal, where electrons alone have kinetic energy proportionalto the plasma energy. The first plasma of the plasma pulses generated isgenerally a non-thermal plasma where the electrons of the plasma have ahigher kinetic energy than the ions and molecules of the plasma. Thermalplasmas are generated from non-thermal plasmas as energy added to theplasma in the form of current and voltage increased the kinetic energyof the charged particles until they reach the same kinetic energy as theelectrons. Thermal plasma are more common in alternating current (AC)and long lifetime plasmas, but can occur in DC plasmas and pulsedplasmas where the dielectric is sufficiently heated before the plasma isinitiated (either by environmental heating or by previous plasmaproduced through the same dielectric). For a thermal plasmaapproximation as shown in Equation 18 below:T _(a) =T _(c) ≈T _(h) =T _(e)  (18)Where particle temperatures include anion temperature T_(a) and cationtemperature T_(c). Both anions and cations are heavier (i.e. moremassive) then electrons and are approximately equal to a heavy particlekinetic energy T_(h). Energy is added to the motion of the chargedparticles by the electric field based on magnitude of the charge notpolarity.

Reaction rate constants for products generated in a plasma or at thequenching of the plasma depend on both the temperature of theplasma—electron temperature and heavy particle temperature—and upon thetotal ionization. By determining the reaction rates based on chemicalconcentrations in the drilling mud, the plasma temperatures can bemonitored.

The average plasma energy

E

is related to both the energy applied to the plasma and to the electrontemperature. The plasma power is related to the potential energydifference over the plasma (in Volts) times the work of moving thecurrent (in Amperes) through the electric field. Power and energy arerelated, where power is energy per unit time (such as Watts), as shownin Equations 19 and 20 below.

$\begin{matrix}{{Power} = {\frac{Energy}{Time} = \frac{\left\langle E \right\rangle}{\Delta t}}} & (19)\end{matrix}$ $\begin{matrix}{{Power} = {{\frac{\partial}{\partial t}{Energy}} = {\frac{\partial}{\partial t}\left\langle E \right\rangle}}} & (20)\end{matrix}$Where power can also be represented as P, energy as E, average energy as

E

, and where t is time.

Reaction rates are a function of plasma temperature (which is ameasurement of plasma energy), which means that plasma temperature canbe calculated or correlated to measured reaction rates. Plasma power canbe approximated from the power added to the system, and from theapproximate plasma power and the plasma duration and an average plasmaenergy can be calculated. By comparing these two measures of plasmaenergy, the energy system can be checked for energy loss (i.e. energylost to the formation can be detected). Either method can be used toapproximate the other.

At block 308, the chemical composition of the drilling mud returning tothe surface is analyzed. For example, with reference to FIG. 1, theinstrumentation 161 can perform the analysis. The drilling mud caninclude both chemical reaction products and formation fluid acquireddownhole, as well as solids in the form of formation cuttings. Thedrilling mud can be separated by phase, where cuttings and other solids(such as debris from the surface like gloves, bolts, etc.) are removed.To illustrate, a shaker and/or screen can receive the drilling mud fromdownhole and separate the cuttings and other solids from the drillingmud. For example, with reference to FIG. 1, the fluid recondition system142 can perform this separation. The instrumentation 161 analyzes thesolids at block 310 of FIG. 3B. The drilling mud logging systemseparates dissolved gasses via low-temperature or low-pressureseparation from the hydrocarbon liquids. The gasses are then analyzed atblock 316 of FIG. 3B, before being fed to a flare for disposal or safelystored. A portion of the cleaned drilling mud fluid can be diverted toallow the instrumentation 161 to analyze this fluid for chemicalcomposition at block 314 of FIG. 3B.

At block 309, the chemical concentration of the reaction product isdetermined. For example, with reference to FIG. 1, the computer 162 canmake this determination based on the instrumentation 161 or the analysissystem 160. The chemical concentration can be measured in weight pervolume (such as grams per liter g/L), moles per volume (such as molesper liter mol/L), weight percent (such as nanograms per milliliterng/mL), parts per million (ppm), mole percent or mole fraction (such asmol compound/mol total or mol %), etc. The chemical concentration can bemeasured for a specific amount of drilling fluid, or as a function ofdrilling rate or time.

At block 310, the cuttings can be analyzed to determine the volume ofrock returned to the surface. For example, with reference to FIG. 1, theinstrumentation 161 can analyze the cuttings. Methods of cuttingmeasurement include optical scanning and image processing to determineparticle size distribution, weighing of cuttings, and calculating volumebased on a measured density (where the density is measured using a coresample or periodically for each formation layer), or via a large boreCoriolis density meter.

At block 312, porosity is determined based on the measurement ofcuttings that occurred at block 310. For example, with reference to FIG.1, the computer 162 can make this determination. The computer 162 canreconstruct the total volume of rock removed from the formation. Thecomputer 162 can also compare that volume as a function of time to thedrilling rate to determine the ratio of rock to pore space in theformation layer being drilled. The pore fraction ø is given by Equation21:

$\begin{matrix}{\phi = \frac{V_{v}}{V_{T}}} & (21)\end{matrix}$Where the pore fraction ϕ is a dimensionless number representing theportion of the rock volume occupied by pores and where V_(T) is thetotal volume and V_(V) is the void volume. Void volume can be correlatedto pore shape, pore size, and pore throat size (where pore throat sizeis a determining factor in permeability).

Porosity and permeability of the formation information can be determinedin traditional mud logging from information about changes in the volumeof drilling fluid and from measurements on the size and volume ofcuttings. The plasma reaction downhole in pulse power drilling convertsa portion of the drilling fluid and formation fluid to gas. Once themass balance of the reaction is determined, the original volume of fluiddownhole is determined. Based on the volume calculation, the drillingmud volume is further subtracted and the remaining volume is a measureof formation fluid volume as a function of drilling depth. By accountingfor formation fluid volume per unit of depth drilled, the percentage offormation rock that constitutes formation fluid space is calculated as ameasure of porosity. The volume of rock fragments measured at thesurface and the calculate pore volume equal the total volume drilled, asa function of time. Each method can therefore function as a check on thevalue of the other.

At block 330, permeability is determined based on porosity andelectrical characteristics of plasma discharge, as will be discussedlater. For example, with reference to FIG. 1, the computer 162 can makethis determination.

At block 314, the chemical composition of the fluid is determined. Forexample, with reference to FIG. 1, the computer 162 can make thisdetermination. The chemical composition of the fluid can include varioushydrocarbons and water. The computer 162 can determine which chemicalsare present and their concentration levels. The computer 162 can makethis determination using the instrumentation 161 that can includeapplication of gas chromatography, liquid chromatography, massspectrometry, absorption or emission spectrometry, nuclear magneticresonance spectrometry (NMR), or the like.

At block 316, the molar concentrations of gasses produced by the plasmareaction is determined. For example, with reference to FIG. 1, thecomputer 162 can make this determination. The molar amount of gasproduced can be determined based on the volume of gas detected at thesurface, using the ideal gas law where each mole of gas corresponds to22.4 at standard temperature and pressure (STP).

At block 318, the formation fluid concentrations are determined based onthe concentrations of species in the drilling mud and estimatedstoichiometry of a chemical reaction. This chemical reaction may be morespecifically a dehydrogenation reaction, where hydrogen gas is producesfrom hydrocarbons as they form more saturated bonds (i.e. more doublebonds). For example, with reference to FIG. 1, the computer 162 canperform this estimation. The computer 162 can determine the change indrilling mud species concentration by subtracting the concentrations ofspecies found in the drilling mud pumped downhole (from block 302, 308,or 309 depending on drilling rig set up). Based on the change inconcentration that corresponds to the influx of formation fluid andchemical reactions generated by the plasma in the fluid at the drillbit, the computer 162 can solve the system of equations corresponding tothe stoichiometric relationships and to the reaction rate equationsbetween the products and the potential reactants. For known or solvablestoichiometry, reactant concentrations can be calculated directly. Formost systems, the stoichiometric equations generate a set of solvableequations with more degrees of freedom than encompassed by productconcentration alone. For these systems, estimated reaction rateconstants and reaction kinetics can be applied in order to determinereactant concentrations.

Drilling mud for traditional mechanical drilling requires propertiesthat promote mechanical drilling and support pore pressure: i.e.density, viscosity, etc. Drilling mud for pulse power drilling is alsoan electrical transportation medium, which makes electrical properties,such as dielectric constant, breakdown voltage, resistivity, etc.important qualities. Both electrical and physical properties depend onchemical concentration of the constituent molecules are particulates ofthe drilling mud which is monitored in traditional mud drilling. Mudlogging for pulse power drilling can also include calculation of thestoichiometry and reaction rate of the chemical reactions occurringdownhole.

The rate at which a chemical reaction takes place, i.e. the rate atwhich reactants turn into products, is given by a generalized reactionrate, which depends on a reaction rate constant k(T) and on theconcentration of reactants (usually in units of moles per unit volume).The reaction rate constant k can itself be a function of temperature,pressure, and activation energy. The reaction rate for a generalizedm+n^(th) order reaction is shown in Equation 22, below, for a ratelimiting step involve molecules of species A and B.r=k(T)[A]^(m)[B]^(n)  (22)Where r is the reaction rate, k(T) is the reaction rate constant, A andB are reactant molecules and the rate limiting step involves m moleculesof reactant A interacting with n molecules of reactant B, such as for areaction mechanism described by a rate-limiting intermediate step shownin Equation 23 below:m·A+n·B→q·P  (23)Where m molecules of A and n molecules of B react to form q molecules ofan example product molecule P.

The order of the reaction (zeroth order, first order, etc.) depends uponthe reaction mechanisms and the rate limiting step in the reaction andhow many and which species of molecules participate in the rarest orslowest collision. The rate limiting step is usually the slowest step ofthe elementary or intermediate steps that make up the reactionmechanism. For many chemical reactions, the reaction mechanism or theset of intermediate steps that occur when reactants become products hasa single step or portion that is observably slower than all other steps.This step functions as a bottleneck or limit on the total reaction speedand is therefore known as the rate limiting step. For a reaction withmultiple intermediate steps, the rate limiting step can depend on acatalyst molecule that is not a reactant or a product. For directcurrent (DC) plasmas with lifetimes in the microsecond (μs) to secondrange, many hydrocarbon formation reactions depend on intermediate stepsinvolving hydroxyl free radicals, carbonyl free radicals or other freeradicals with very short lifetimes, where free radical formation istherefore the rate determining step. Hydroxyl free radical formation andconcentration is dependent on water concentration, not hydrocarbonconcentration, and upon plasma energy and properties including plasmatemperature and geometry. This gives rise to many zeroth and first orderreaction rates for generation of alkenes, alkynes, aromatics, and otherunsaturated hydrocarbons from alkanes. A zeroth order reaction rate isgiven by Equation 24:r=k(T)[A]⁰ =k(T)  (24)where r is the reaction rate, k(T) is the reaction rate constant for areaction with the rate limiting step that is independent of reactantconcentration and where [A] is a reactant concentration. A zeroth orderreaction rate does not depend on the concentration of the reactants andhas a rate constant with units of moles per second (mol/s) orequivalent. A first order reaction rate depends in the first order (i.e.[A]¹) on a reactant and has a rate constant with units s⁻¹ orequivalent, as is shown in Equation 25, below.r=k(T)[A]  (25)Where r and k(T) are the reaction rate and reaction rate constant,respectively.

The reaction rate constant k(T) depends on temperature and can beapproximated using the Arrhenius equation, as shown in Equation 26below:k(T)=Ae ^(−E) ^(a) ^(/RT)  (26)The Arrhenius equation relates the reaction rate constant k to theactivation energy E_(a), the absolute temperature T in Kelvin, theuniversal gas constant R, and a pre-exponential factor A representingthe fraction of molecular collisions resulting in the chemical reactionout of all molecular collisions of the species of the rate limitingstep. Alternatively, the Boltzmann constant k_(B) can be used in placeof R if the activation energy E_(a) is also in units of k_(B)T. Anexponential fitting factor β can also be used to correct modeled data toexperimental data, as is shown for Equation 27.

$\begin{matrix}{{k(T)} = {{A{Exp}}\left\lbrack {- \left( \frac{E_{a}}{RT} \right)^{\beta}} \right\rbrack}} & (27)\end{matrix}$Where β is a dimensionless fitting factor used to relate reaction rateconstants to observable reaction rates, as a function of temperature.

Formation fluid can be approximated to a first order as containingalkanes, naphthenes (which is a generic name for the family ofcycloalkanes), and water. Alkanes, which the general chemical formulaC_(n)H_(2n+2), contain single carbon to carbon bonds (σ bonds) between nsp³ hybridized carbon atoms. Alkanes are saturated hydrocarbons whichcontain no carbon-carbon double bonds (π bonds) but are rather fullhydrogenated—that is the carbon backbone or carbon chain is bonded tothe maximum number of hydrogen atoms possible. Naphthenes, which arecyclic alkanes where the carbon chain loops back on itself, have thegeneral chemical formula C_(n)H_(2(n+1−r)) where n is the number ofcarbons in the cycloalkane and r is the number of rings in the naphthenemolecule. Formation fluid can also contain water, such as salt water,when emanating from water rich rock formations or strata. Thegeneralized chemical equation for the plasma reaction is approximated byEquation 28, below:A_(n)·C_(n)H_(2n+2)+B_(n,r)·C_(n)H_(2(n+1−r))+D·H₂O→E_(n)·C_(n)H_(2n+2)+F_(n,r)·C_(n)H_(2(n+1−r))+G_(n)·C_(n)H_(2n)+I_(n)·C_(n)H_(2n−2)+J·CO₂+K·O₂+L·H₂  (28)where A_(n) is the stoichiometric coefficient for a reactant alkane of ncarbon atoms with the molecular formula C_(n)H₂₊₂, B_(n,r) is thestoichiometric coefficient for a n carbon naphthene reactant moleculewith r rings with the molecular formula C_(n)H_(2(n+1−r)), E_(n) is thestoichiometric coefficient for a product alkane of n carbon atoms withthe molecular formula C_(n)H_(2n+2), F_(n,r) is the stoichiometriccoefficient for a n carbon naphthene product molecule with r rings withthe molecular formula C_(n)H_(2(n+1−r)), G_(n) is the stoichiometriccoefficient for an n carbon alkene with molecular formula C_(n)H_(2n),and I_(n) is the stoichiometric coefficient for an n carbon alkyne withmolecular formula C_(n)H_(2n−2). D is the stoichiometric coefficient forwater (H₂O), J is the stoichiometric coefficient for carbon dioxide(CO₂), K is the stoichiometric coefficient for oxygen (O₂), and L is thestoichiometric coefficient for hydrogen (H₂).

The stoichiometric coefficients for each of the hydrocarbon species(i.e. A_(n), B_(n,r), E_(n), F_(n,r) G_(n) and I_(n)) depend both on thenumber of carbons of the type of hydrocarbon (i.e. n) and the isomer (oratomic arrangement) of those carbons, but can be approximated asindependent of isomeric configuration in order to simplify measurements.Table 1, below, contains names and formulas alkanes, alkenes, andalkynes as a function of the number of carbons they contain. As themolecules become larger (i.e. as n increases) the number of isomermolecules for each chemical formula increase, where isomers are variousphysical arrangements and chemical bonds possible for the same atoms.For n>2, polyunsaturated hydrocarbons also occur (i.e. hydrocarbons withtwo or more double bonds). Unsaturated hydrocarbons such as alkanes, arecarbon molecules that contain only hydrogen and carbon and have themaximum number of hydrogen constituents possible for the given amount ofcarbon atoms. The ability to detect or differentiate hydrocarbons,including isomers, from one another depends on the specificity ofinstrumentation and is non-trivial.

As the number of carbons grows, the number of isomersincreases—eventually increasing exponentially. For a hydrocarbonconsisting of 40 carbon atoms and 82 hydrogen atoms, there are largerthan 62 million isomers. Decane, C₁₀H₂₂, has 75 isomers. In someembodiments, hydrocarbons with large numbers of isomers are grouped bycarbon atom amount instead of determined or quantified by individualisomer. Alkenes and alkynes have more isomers than alkanes because thelocation of the double or triple bond contributes to isomermultiplicity. In some embodiments, the number of isomers consideredlarge is over ten. In other embodiments, hydrocarbon molecules with tenor more carbon atoms can be considered to have large numbers of isomers.Hydrocarbons can be grouped by those with large numbers of isomers,which can be measured as a function of carbon count and not individuallyresolved, or can be grouped into isomeric groups that can be resolved bymolecular weight or gas chromatography or another separation analysis.

TABLE 1 Common Hydrocarbons N Formula Alkane Isomers Formula AlkeneIsomers Formula Alkyne Isomer 1 CH₄ Methane 1 2 CH₃CH₃ Ethane 1 CH₂═CH₂Ethene 1 HC≡CH Acetylene 1 3 CH₃CH₂CH₃ Propane 1 CH₃CH═CH₂ Propene 1HC≡CCH₃ Propyne 1 4 CH₃(CH₂)₂CH₃ Butane 2 CH₃CH₂CH═CH₂ Butene 4CH₃C≡CCH₃ Butyne 2 . . . 40 C₄₀H₈₂ Large C₄₀H₈₀ Large C₄₀H₇₈ Large

In general, the products of the chemical reaction of Equation 28 havehigher enthalpy or energy of formation that the reactants, which will bedescribed in more detail below in reference to FIGS. 5A-5B. This higherenergy corresponds to the energy balance, where the energy added to theplasma is stored in higher order chemical bonds and endothermicreactions are favored by high energy transition states.

The stoichiometry balance of the reaction can be determined based on themeasured composition of the drilling fluid. The drilling fluid ismeasured as it exits the wellbore—hydrocarbon concentrations aremeasured as are types and volumes of evolved gasses. The composition ofthe drilling mud pumped downhole is either measured as circulates backdownhole, or the measured composition of the drilling mud returned tothe surface is set as the drilling mud concentration when that mudrecirculates into the wellbore. In either case, an initial drilling mudconcentration is subtracted from a final drilling mud concentration,which generates the change in concentration for various speciesoccurring downhole.

To help illustrate, FIG. 4A depicts an example line graph of thereaction kinetics and reaction path of an example plasma-mediatedchemical reaction, according to some embodiments. In particular, FIG. 4Adepicts a graph 400 having a y-axis for energy 402 and an x-axis for areaction pathway 404. The graph 400 depicts example reaction kineticsand molecular energies for example reactants and products of a pulseplasma. The plasma energy, which is the energy added to the systemconsumed to generate the plasma, can create highly energized particles,both kinetically energized and energized electronically above the groundstate. Energized molecules and atoms therefore interact more frequentlyand can form transition states favorable to reaction. The graph 400depicts an example reaction pathway (also known as a reaction path) fora set of reactants, their intermediate transition state, and the finalproducts of the example reaction. Activation energy E_(a) 412 is theenergy per set of reactants or per reaction needed to reach transitionstate 410, where the transition state 410 is a complex formed betweenthe atoms of the reactant molecules that is the highest energy stateduring the chemical transformation from the reactant species to theproduct species.

For most of the hydrocarbon reactions occurring in the plasma, reactionproducts 408 will have a greater enthalpy of formation 414 thanreactants 406 (i.e. higher energy 402). Enthalpy of formation is ameasure of the energy contained within a molecule as a sum of theenergies contained within the chemical bonds between the constituentatoms. The plasma energy can be defined as the total energy in theplasma. The plasma energy added to the fluid is stored in higher ordercarbon bonds. Each molecular reaction can store the enthalpy offormation 414 (as an amount of energy) within the reaction products' 408chemical bonds. The reaction energies include the activation energyE_(a) 412 and the enthalpy of formation 414, and can be defined as theenergy needed for a set of reactants 406 to reach the transition state410 or stored in the reaction products 408. The reaction energy can bemeasured on a per reaction or molar basis. When species collide andreact, the frequency at which the transition state 410 arrangement ofthe hydrocarbon is reached is a function of the kinetic energy added tothe molecule through absorption of a photon, stabilized via hydroxyl, orother catalysis processes. In a plasma, the kinetic energy of theparticles is high because the plasma energy is high. The plasma energyis a measure of the kinetic energy of the particles and molecules withinthe plasma, and higher energy transition states are allowed (and occurmore frequently), as shown along the reaction pathway 404.

In the graph 400, the reaction pathway 404 is a simplified timeline ofthe reaction, going from the reactants 406 to the reaction products 408(showing an intermediate step—the transition state 410). Reactionmechanisms, which include possible reaction pathways and intermediatesteps, can be much more complicated. A reaction mechanism can be definedas the series of steps and chemical rearrangements that occur during areaction at a molecular level, where reactants transform into products.A reaction mechanism may include intermediate steps, some of which canlead to formation of multiple different reaction products. A reactionpath or reaction pathway can be defined as the method or steps of thereaction mechanism which lead from a set of reactants to a set ofreaction products. A reaction can have more than one pathway thatgenerates identical reaction products from reactants (as will bediscussed in reference to FIG. 4B), and each pathway can have adifferent activation energy and reaction rate. For instance, catalystscan stabilize transition states thereby lowering activation energies andincreasing the speed of a given reaction rate, but even in catalyzedreactions a portion of the products may be generated through the higherenergy uncatalyzed transition state. Reactions, including intermediatereaction steps, can also be reversible which means that a significantportion of the reaction products re-react to re-from the reactantspecies. Dehydrogenation reactions tend to be irreversible because thegaseous reaction products quickly dissociate from the hydrocarbonspecies, but transition states in dehydrogenation reactions are likelyto form reaction products or to re-form reactants.

Plasma energy (of the entire plasma) and reaction energy (of eachindividual chemical reaction) can be correlated—higher plasma energyfavors reactions with larger activation energies and greater enthalpy offormation. The concentration of product species multiplied by theenthalpy of formation of each species generates a total reaction energyfor the chemical reactions within the plasma that can be compared to theplasma energy.

To further illustrate, FIG. 4B depicts example reactants and products aswell as example reaction pathways, according to some embodiments. FIG.4B depicts examples of species of reactants 406, examples of reactionpathways 404, and examples of species of reaction products 408. In orderto calculate the formation fluid concentration, a set of equations basedon reaction rate constant and final or product concentration can begenerated. For a generic product molecule, P, of the first orderreaction shown in Equations 29 and 30, the final concentration [P] canbe known and measured at the surface during drilling mud analysis.R→P  (29)

$\begin{matrix}{r = {{{k(T)}\lbrack R\rbrack} = {{- \frac{d\lbrack R\rbrack}{dt}} = \frac{d\lbrack P\rbrack}{dt}}}} & (30)\end{matrix}$Where R is a generic reactant and P is a generic product of the firstorder reaction of Equation 29. [R] is a concentration of molecule R, [P]is a concentration of molecule [P], r is a reaction rate, and k is areaction rate constant which is a function of temperature T.

Product species P can include at least one species from at least one ofalkenes 440, alkynes 442, polyunsaturated hydrocarbons 444, and any ofthose species included corresponding to reactant species R. Reactantspecies R can include species from at least one of the alkanes orsaturated hydrocarbons 420, the naphthenes 422, or the aromatics andcyclic alkenes 424, as can be found in the formation fluid. If thereaction rate constant k(T) is also known, the reactant concentration[R] (which is the formation fluid concentration) for a generic product Pis directly calculable according to Equation 31-33 below:

$\begin{matrix}{\lbrack P\rbrack = {{r*{\Delta t}} = {{{k(T)}\lbrack R\rbrack}*{\Delta t}}}} & (31)\end{matrix}$ $\begin{matrix}{\lbrack P\rbrack = {{\int{rdt}} = {\int{{{k(T)}\lbrack R\rbrack}{dt}}}}} & (32)\end{matrix}$ $\begin{matrix}{\lbrack R\rbrack = \frac{\lbrack P\rbrack}{{k(T)}*{\Delta t}}} & (33)\end{matrix}$where the concentrations of P and R change as the reaction occurs.Concentration changes may be large enough that the change in reactantconcentrations favors the use of integrals (as shown in Equation 32)instead of discrete analysis (as shown in Equations 31 and 33). Theinstantaneous product concentrations may not be known, as can occur whendrilling mud circulation prevents instantaneous measurement of chemicalreaction products. If the instantaneous concentrations are not known,the reaction rate and reactant concentration can be approximated usingintegral approximation, such as for an exponential concentrationapproximation, or discrete analysis.

A product molecule(s) P can be generated from a reactant molecule(s) Rvia an example photon-mediated reaction pathway 430 or an examplehydroxyl-mediated pathway 432. The ratio between reactions catalyzed bylight and those catalyzed by hydroxyl free radicals can correspondroughly to the ratio between plasma arc and plasma spark.

For the set of alkane dehydrogenation reactions (which can be consideredto be the opposite of cracking reactions) encompassed by Equation 28(set forth above), the molar concentrations of hydrogen, carbon dioxide,and oxygen gases can be determined at the surface. From the oxygen massbalance of the chemical reaction, the relationship between coefficientsD, J, and K is determined, as shown in Equation 34.D=2(J+K)  (34)Where D is the stoichiometric coefficient for water, J is thestoichiometric coefficient for carbon dioxide, and K is thestoichiometric coefficient for hydrogen as defined in the chemicalreaction of Equation 28. This allows the initial concentration of waterto be calculated based on the measured molar concentrations of carbondioxide and oxygen measured at the surface, as is shown in Equation 35,below:[H₂O]=2([CO₂]+[O₂])  (35)

The mass balance of the carbon and hydrogen atoms can be complicated bythe multiplicity of the hydrocarbon species. The chemical analysis doesnot necessarily determine a concentration for each isomer of thesaturated and unsaturated hydrocarbons. Isomer concentrations, whereavailable, can refine available mass balance equations. The chemicalanalysis equipment can identify concentrations of hydrocarbons as afunction of n and carbon to hydrogen (C/H) ratio with great specificity.The total carbon balance is given by Equation 36 and the total hydrogenbalance is given by Equation 37.

$\begin{matrix}{{{\sum\limits_{i = 1}^{n}{i*A_{i}}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{r}{i*B_{i,j}}}}} = {{\sum\limits_{i = 1}^{n}{i*E_{i}}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{r}{i*F_{n,j}}}} + {\sum\limits_{i = 1}^{n}{i*G_{i}}} + {\sum\limits_{i = 1}^{n}{i*I_{i}}}}} & (36)\end{matrix}$ $\begin{matrix}{{{\sum\limits_{i = 1}^{n}{2\left( {i +} \right)*A_{i}}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{r}{2\left( {i + 1 - j} \right)*B_{i,j}}}} + {2D}} = {{\sum\limits_{i = 1}^{n}{2\left( {i + 1} \right)*E_{i}}} + {\sum\limits_{i = 1}^{n}{\sum\limits_{j = 1}^{r}{2\left( {i + 1 - j} \right)*F_{n,j}}}} + {\sum\limits_{i = 1}^{n}{2i*G_{i}}} + {\sum\limits_{i = 1}^{n}{2\left( {i - 1} \right)*I_{i}}} + {2L}}} & (37)\end{matrix}$Again, the stoichiometric coefficients for each of the hydrocarbonspecies (i.e. A_(n), B_(n,r), E_(n), F_(n,r), G_(n) and I_(n)) come fromEquation 28 previously and represent the total equation mass balance foreach of the carbon species with n carbons.

The stoichiometric coefficients for the hydrocarbon species—A_(n),B_(n,r), E_(n), F_(n,r), G_(n) and I_(n)—appear in both the carbon massbalance and the hydrogen mass balance (which also includes coefficientsD and L). The stoichiometric coefficient D, J, and K are related basedon the oxygen balance previously discussed in relation to Equations 34and 35. The stoichiometric coefficients are constrained by theseequations, which becomes a solvable system of equations for coefficientsof the reaction.

The final concentrations of species can also be known, where [CO₂],[O₂], [H₂] can be measured directly. If not all water is consumed duringthe plasma-driven chemical reaction, the initial concentration of watercan be calculated directly from the gaseous product concentration andthe final concentration of water in the drilling fluid, given byEquation 38:[H₂O]_(initial)=[H₂O]_(final)+2([CO₂]_(final)+[O₂]_(final))  (38)where initial denotes the concentration in the formation fluid anddrilling mud downhole before the plasma reaction, and final denotes theconcentrations measured in the drilling fluid after the reaction (eitherat the surface or with analysis equipment downhole). If the drilling mudcontains water when it is pumped downhole, the formation fluid's waterconcentration can then be given by Equation 39, which accounts for achange in water concentration due to formation fluid influx.[H₂O]_(initial)=Δ[H₂O]_(drilling fluid)+2([CO₂]_(final)+[O₂]_(final))  (39)Where the change in drilling concentration in the drilling fluid isrepresented by Δ, which is the change in the water concentrationmeasured in the drilling fluid before and after the reaction.

Product hydrocarbon concentration [C_(n)H_(2n+2)], [C_(n)H_(2(n+1−r))],[C_(n)H_(2n)], and [C_(n)H_(2n−2)] can also be calculated or determined,based on direct measurement or inference. For example, with reference toFIG. 1, the computer 162 can perform this operation. The known andunknowns together create a system of equations where the initialformation concentrations are solvable. Further, reaction kinetics allowrefining of the concentrations based on known product concentration andcalculable reaction rates, as shown in Equations 24-25 (set forthabove).

If reaction rates are known (i.e. can be calculated based on productconcentrations as a function of time) and the reaction order of the ratelimiting step (i.e. first order, second order, etc.) is known, thenexact concentrations of reactants are calculable from productconcentrations. For hydrocarbon dehydrogenation, most reaction rates arefirst order or zeroth order. Zeroth order reactions depend on time, noton reactant concentration (to a first approximation). Productconcentrations follow Equation 40.[P]=k(T)*Δt  (40)Where [P] is the concentration of a generic product molecule P and Δt isthe lifetime of the reaction. These types of reaction kineticscorrespond to chemical reactions dependent on free radicals, equilibriumrearrangement at high temperature (such as for hydrocarbon isomers inequilibrium), and for catalyzed reactions where k may be zeroth orderwith respect to reactants but depend on the concentration of a catalyst.For first order reactions, product concentrations can be related toreactant concentrations as shown in Equation 41.[P]=k(T)[R]*Δt  (41)Where [R] is the concentration of a generic reactant molecule R. Wherethe concentration of R is also a function of time, this equation becomesEquation 42:[P]=∫k(T)[R]dt  (42)In general, the concentration of a first order reactant as a function oftime is given by solving the rate equation to get Equation 43, below:[R]=[R]₀ e ^(−k(T)*t)  (43)Where [R]₀ is the initial concentration of generic reactant R, k(T) isthe reaction rate constant, and t is time. Substituting Equation 43 intoEquation 42 yields equation 44:[P]=∫k(T)[R]₀ e ^(−k(T)*t) dt=k(T)[R]₀ ∫e ^(−k(T)*t) dt=[R]₀ e^(k(T)*t)  (44)Where this relationship holds when one molecule of reactant R yields onemolecule of product P. The product concentration for first orderreactions can be similarly related to reactant concentrations fordifferent stoichiometric relationships as well.

By correlating reaction rate constant to temperature and plasma power,rate constant values are further refined. The rate constant for a plasmareaction can be a function of temperature, plasma power, and activationenergy. Activation energy for transition states are known. Determinationof a reaction rate constant for a first order reaction can be made byvarying the plasma power (where temperature is constant, and activationenergy is a function of the transition state and therefore constant forthe specific reaction mechanism). This is shown in Equations 45-47,below, where the reactant concentration [R] is a function of theformation and does not vary over the time scale of the power analysis.

$\begin{matrix}{\lbrack P\rbrack_{1} = {{{{k\left( {T,{PW}_{1}} \right)}\lbrack R\rbrack}*{\Delta t}} = {\lbrack R\rbrack_{0}e^{{k({T,{PW}_{1}})}*t}}}} & (45)\end{matrix}$ $\begin{matrix}{\lbrack P\rbrack_{2} = {{{{k\left( {T,{PW}_{2}} \right)}\lbrack R\rbrack}*{\Delta t}} = {\lbrack R\rbrack_{0}e^{{k({T,{PW}_{2}})}*t}}}} & (46)\end{matrix}$ $\begin{matrix}{\frac{\lbrack P\rbrack_{1}}{\lbrack P\rbrack_{2}} = {{{Exp}\left\lbrack {k,{\left( {T,{PW}_{1}} \right) - {k\left( {T,{PW}_{2}} \right)}}} \right\rbrack} = {\left. {f\left( {{Exp}\left( \frac{{PW}_{1}}{{PW}_{2}} \right)} \right)} \right.\sim{f({PW})}}}} & (47)\end{matrix}$Where P represents the product concentration and PW represents theplasma power. PW is used so that power is not confused with eitherproduct concentration [P] or pressure as used previously. Subscripts 1and 2 denote a first power setting and its corresponding concentrations,temperature, and time, and a second power setting and its correspondingconcentrations, temperature, and time. Tis temperature and t representstime. The power analysis can be simplified if all time and temperaturesremain constant while power is varied, so that the relationship betweenk(T) and power can be explored.

The dependence of the rate constant on plasma power can be determinedfrom the product concentrations as a function of power. Once therelationship between rate constant k and plasma power is known, then therelationships between reactant concentration and product concentrationcan generate another set of equations that further restrict the degreesof freedom of the system.

The reaction rate constants can also vary by plasma type. For example,the reaction rate constants for plasma arcs can be different than thereaction rate constants for plasma sparks even for similar products andreactants over the same rate limiting step. Certain reaction productsare favored by different types of plasma, as previously discussed inrelation to hydroxyl free radical formation and hydroxyl-mediated versusphoton-mediated reaction pathways. Reaction rate constants for each typeof plasma can be determined via at least one of a plasma power analysisor a spark versus arc ratio analysis.

The relationship between the product and reactant concentrations canthereby be constrained enough to allow for solving for reactantconcentrations based on measured product concentrations and plasmaparameters. These solutions can be determined directly, with sufficientproduct information, or can be solved iteratively or by machine learningapplied to a body of data.

Returning to operations of FIG. 3 at block 319, the fluid loss or influxis estimated based on the concentration of species in the drilling mud.Influx of formation fluid into the wellbore or loss of drilling mud tothe formation can be further determined based on the ratio of plasmareaction products. For example, with reference to FIG. 1, the computer162 can perform this estimation. The computer 162 can determine a ratiobetween hydrogen and small molecular weight hydrocarbons or betweenhydrogen and aromatics or between small molecule alkanes and aromaticsin order to estimate the amount of drilling fluid lost to the formationor the fluid volume gained due to an influx of formation fluids. Thecomputer 162 can also estimate the total volume of drilling fluidreturned to the surface using instrumentation 161 or fluidreconditioning system 142.

Drilling fluid or mud is necessary to maintain pressure downhole abovethe pore pressure of the formation. If the pressure downhole is belowthe pore pressure of the formation, the pressure downhole can beconsidered too low as gas and fluid can enter the wellbore from thesurrounding formation. For reactive gases like H₂ and H₂S, entrance ofdissolved gasses into the drilling mud can lead to corrosion downholeand can lead to violent or explosive evolution as the drilling mud movestowards lower pressures at the surface. If the pressure downhole isabove the formation fraction pressure, the pressure downhole can beconsidered too high as the wellbore or wellbore walls may collapse asthe formation is fractured or destroyed by drilling mud forces intoweaker strata. Monitoring the amount or volume of drilling mud returnedto the surface allows mud logging to estimate the influx of fluid intothe wellbore or the loss of fluid to the formation. Pulse power drillingcan complicate this determination because the chemical reactionsdownhole generate gaseous products, in addition to vaporization of water(from aqueous fluids) and carbon dioxide and the like dissolved inhydrocarbon fluids. Many of the gasses generated downhole via the plasmawill dissolve, under pressure, back into the drilling fluid (which canbe assumed to be a non-Newtonian high temperature and high-pressurefluid) as the plasma is quenched. The gaseous products are detectablevia low pressure or low temperature gas extraction, or distillation,from the drilling fluids.

Further, influx and loss can be detected by a shift in the chemicalcomposition of the drilling fluid, or product concentrations in thedrilling fluid. When drilling fluid is lost to the formation, that losscan result in a steadier drilling fluid chemical composition. Thedrilling fluid returned to the surface can significantly match thecomposition of the drilling fluid that was pumped downhole. The loss tothe formation limits the amount of hydroxyl free radicals created fromwater molecules available to catalyze the chemical reactions downhole,and therefore slows reaction rates.

In the case of an influx into the wellbore, formation fluid and productconcentration in the drilling fluid can increase. Saltwater flow intothe wellbore can significantly increase the amount of hydrogen gasdetected at the surface. The ions present in the saltwater increase thefractional ionization of the plasma formed downhole. The increase inhydroxyl groups (where water readily decomposes into hydroxyl groups andhydrogen) can increase reaction rates, but significantly increases theproduction of hydrogen molecules at a rate greater than the increase forother products. An influx of gas from the formation increases theconcentration of methane and short carbon products. Hydrocarbon gas isalready heavy in small molecular weight carbon species (i.e.approximately n≤10), and these reactants tend to crack and form smallunsaturated molecules or merge but remain small in the presence ofcatalyst. An influx of oil from the formation, where oils contain highmolecular weight hydrocarbons, can lead to an increase in the complex,aromatic, and unsaturated product species and concentrations.

The total volume of drilling fluid or drilling fluid level in the mudpit remains a valuable method of measuring formation loss and influx.However, monitoring the products of the chemical reactions downholeenable mud logging to further record information about the formationfluid.

At block 320, the determined formation fluid concentrations are refinedby correlating reaction rates to plasma energy. Reaction ratecalculations can be applied in order to generate additional equations tobetter define the system of linear equations to generate a definitesolution. For example, with reference to FIG. 1, the computer 162 canperform this operation. Many of the reaction pathways can sharetransition states, where transition states determine the activationenergy E_(a) of a reaction pathway. For reactions with known activationenergy, the reaction rate constant can be calculated directly from themeasured temperature at the plasma (based on the Arrhenius or similarequation) or can be estimated based on a plasma power analysis performedin the wellbore previously.

Free radicals are high energy and unstable, especially in alkanes. Thehydroxyl radical has the longest lifetime of the free radicals produceddownhole. The chemical reactions occur at equilibrium in the plasma,where high velocity electrons enable formation of transition states. Forphoton-emitting plasmas, photons can generate excited states inside theplasma and in surrounding fluid. Without regard to which excitationmechanism generates the transition state, products are generated as theplasma is quenched and further chemical transitions become energeticallyunfavorable.

Further information is gained via periodic off bottom plasma generationevents. The drilling bit is retracted from the wellbore bottom andsuspending in the wellbore surrounded by drilling fluid (or onlypartially introduced into the well) and a plasma is generated, thecontribution of the drilling fluid to the reaction rate and productspecies is then measured. The drilling fluid plasma products is thensubtracted from the total product concentration measured at the surface,in order to selectively identify the reaction products corresponding tothe formation and formation fluid at the wellbore bottom. The off bottomanalysis can also be conducted for a variety of plasma powers, in orderto determine the arc vs. spark ratio of each plasma power setting whichcan be extrapolated as the arc vs. spark ratio for the wellbore bottomplasma in the formation.

At block 322, a relation between the plasma arc and the plasma spark iscalculated based on concentrations, gas species, and volume of thedrilling mud. For example, a ratio between the plasma power thatgenerates the plasma arc and the plasma power that generates any plasmasparks can be calculated. For example, with reference to FIG. 1, thecomputer 162 can make this calculation. This relation may be calculatedas a ratio, a fraction, a percentage, or a range. The relation betweenthe arc and spark for the plasma can depend on the power used togenerate the plasma and upon wellbore geometry and dielectriccharacteristics. As discussed in reference to FIGS. 2A-2C (and furtherdiscussed in reference to FIGS. 4A-4B and 5A-5B below), both porosityand permeability along with formation fluid resistivity, can contributeboth to the total dielectric strength between the anode and cathode andto the distribution of plasma arcing vs. sparking. Plasma arcs andplasma sparks can produce distinctive products and the relation of theseproducts can correspond to the relation between the plasma arc andspark. For instance, plasma sparks generate high temperature, morespherical plasma, and vapor bubbles in fluid. Whereas, plasma arcsgenerate lower temperature, more elongated bubbles with longerlifetimes. Certain species, for example, are preferentially formed ineach type of plasma. For example, plasma sparks favor formation ofhydroxyl catalyzed reaction and produce a significant amount ofhydrogen. Whereas, plasma arcs favor photon catalyzed reactions, whereultraviolet (UV) photons especially promote carbon-carbon bond formationespecially cyclic alkanes (naphthenes).

To help illustrate, FIGS. 5A-5B depict example geometric approximationsfor a plasm arc and a plasma spark, respectively. FIG. 5A depicts thegeometric approximation for a plasma arc, according to one or moreembodiments. FIG. 5A depicts a plasma arc 512 between an anode 508 and acathode 510. The plasma arc 512 can be generated as DC plasmadischarges, between the anode 508 and the cathode 510. As shown, theplasma arc 512 appears as jagged emissive paths as the DC plasmadischarges. AC plasma discharges tend to have a softer more even glowand are usually contained by a magnetic field. The plasma arc 512 isvisible because highly energetic electrons and molecules are created,which emit photons as they decay back to their ground states.

Within a plasma, particles can be so energetic that chemical bonds arein flux. The chemical composition of ions and molecules can be set whenthey leave the plasma, either because the plasma is quenched, or becausetheir kinetic energy takes them outside of the plasma bounds. In eithercase, the chemical reactions can occur at the boundaries of the plasmawhere each species no longer experiences the excitation or collisionsfor it to reach a transitional state (as explained in reference to FIGS.4A-4B above). The chemical reaction rates for formation of complexhydrocarbons from alkanes and naphthenes (as described in Equation 28)can depend most closely on the concentration of hydroxyl radicals and onenergetic photons, both of which function as catalysts for suchreactions. As depicted in FIG. 5A, the plasma arc 512 can beapproximated as a cylinder 502 sustained by electrons from the anode 508to the cathode 510 and generate larger, elongated gas-phase bubbles.

FIG. 5B depicts the geometric approximation for a plasma spark,according to one or more embodiments. FIG. 5B depicts a plasma spark 514between the anode 508 and the cathode 510. The plasma spark 514 can begenerated as a DC plasma discharges between the anode 508 and thecathode 510. As shown, the plasma spark 514 appears as a jaggedbranching path surrounding the cathode 510. The plasma spark 514 canrepresent the plasma generated that does not complete the circuitbetween the anode 508 and the cathode 510. Plasma spark 514 is visiblebecause, as for the plasma arc, highly energetic electrons and moleculesare created, which emit photons as they decay back to their groundstates. The plasma spark 514 tends to generate spherical bubbles 504,506 as a result of hydrodynamics.

Each type of plasma also trends towards a different plasma temperature.Plasma arcs have lower electron temperatures than plasma sparks, whereplasma sparks have higher electron kinetic energy because more energy isrequired to create a plasma in the absence of the strong electric fieldbetween the anode and cathode. The individual reactions occurring ineach type of plasma can be the same, but the dominant reactionmechanisms can differ as a result of differences in surface area andtemperature.

Returning to FIG. 3 at block 326, the plasma energy and reaction rateestimates and calculations are updated based on the arc to spark ratio.For example, with reference to FIG. 1, the computer 162 can perform thisupdate. The arc to spark ratio can be estimated and updated, along withthe other reaction and plasma parameters, until the stoichiometricequations balance and concentrations of formation fluid species aredetermined. The computer 162 can determine the reactant concentrationsexactly or to within a preselected error range. Such a determination caninvolve an iteration of all factors, multiple iterations, look up ofreaction rate constants based on plasma power, or based on machinelearning. The computer 162 can maintain a record of the drilling mudspecies concentration before and after the plasma is applied (i.e.before the mud is pumped downhole and then at the surface) in order tocorrectly account for species in the drilling fluid, species in theformation fluid, and the species that are reactants in the plasmachemical reaction (measured as chemical products).

At block 328, the electrical properties of the formation at the drillbit are determined. For example, with reference to FIG. 1, the computer162 can make this determination based on the determination of theformation fluid (found in the pore spaces), the arc versus spark ratio,and the plasma power lost to the formation. The electrical properties ofthe dielectric, including breakdown voltage and resistivity, cancorrelate to fluid and rock properties.

At block 330, the formation permeability is determined based on theporosity determined at block 312 and the electrical characteristics ofthe formation fluid and formation calculated at block 328. For example,with reference to FIG. 1, the computer 162 can make this determination.The permeability can be defined in terms of the interconnectedness ofthe pore spaces, or pore throat size or pore diameter, and in relationto the pore volume.

Permeability is a measure of the formation's or formation strata'sability pore connectivity or ability to transmit fluids and is animportant petrophysical property. The permeability of a formationeffects the dielectric constant of the combined drilling mud, formationfluid, and rock. The permeability of the formation correlates to the arcto spark ratio, where interconnected pores (which are more permeable)are also more conductive. High permeability formation layers can biasarc formation, where the connection between the anode and cathode andcurrent transport between them happens preferentially in the porespaces. Interconnected pores can provide a conductive (or moreconductive) path for electrons, over which the breakdown voltage will bereached more quickly and where the plasma will form. Low permeabilityrocks, where pores are not connected or with smaller pores, willpreferentially form sparks where there is no free electron path betweenthe anode and cathode. Charge carriers in fluids are intrinsically moremobile than charge carriers in solids, especially ionic solids andinsulators.

The combination of porosity and permeability determination allow rockformation type determination. Formation layer type can be determinedbased on lithology related to formational fluid, rock porosity, andpermeability or can be determined based on the characterized formationinformation based on machine learning or discrete analysis.

At block 332, the formation and formation fluid are determined as afunction of depth. For example, with reference to FIG. 1, the computer162 can determine the types of formation and formation fluid type basedon one or more of porosity, permeability, electrical characteristics,and formation fluid composition. The computer 162 can also correlateplasma and chemical parameters to formation layers identified at thedepth of the drill bit. The computer 162 can output a mud log analogousto those obtained for traditional mechanical drilling, or canadditionally output plasma parameters and major product species as afunction of depth.

B. Example Operations for Subsurface Rock Formation Evaluation Based onPlasma Chemistry

During pulse power drilling, the exposed structure of the subterraneanformation can interact with the generated plasma and impact the chemicalreactions downhole. The formation may act as either a catalyst or aninhibitor to either enhance or reduce the rate of chemical reactions asa function of the exposed structure. The exposed structure can functionas a reaction surface or matrix, as nucleation sites, etc., for thedehydrogenation reactions of Equation 28 or for other chemicalreactions, where reaction enablement is based on porosity, surfaceroughness, atomic composition of surface sites, etc. The generatedplasma can interact with the solid material of the formation, asdepicted in FIGS. 2A-2C, where such an interaction can cause a shift inthe chemical reactions that can be correlated to the formation (i.e.formation type, porosity, etc.). The generated plasma can also volatize,vaporize, or liquify portions of the formation material, such aswater-rich clay matrices, carbonate rocks, silica formations, etc. Asthe formation is broken up, particles or vapors containing formationions, atoms, or molecules can become part of the plasma reaction andparticipate as reactants in the chemical reactions downhole.Accordingly, various attributes of the formation (e.g., type offormation) can be determined by analyzing the shifts in the plasmareactions and the products of the plasma reactions due to influence ofthe formation.

FIG. 6 depicts a flowchart of example operations for determining rocktype based on plasma chemistry, according to one or more embodiments.Embodiments of the example operations described and illustrated in aflowchart 600 of FIG. 6 may include operations that are performed by apulse power drilling system 100, as illustrated and described withrespect to FIG. 1 above. However, program code naming, organization, anddeployment can vary due to arbitrary programmer choice, programminglanguage(s), platform, etc. Operations of the flowchart 600 begin atblock 602.

At block 602, pulse power drilling mud logging is performed. The pulsepower drilling mud logging can be performed as depicted in flowcharts300-350 of FIGS. 3A-3B or can be performed in an alternate manner. Thepulse power drilling mud logging can measure formation fluid as afunction of time, which is related to drilling depth in the wellbore viathe circulating drilling mud, and provides information about thechemical composition of drilling fluid which has interacted with anelectric pulse emitted from the drill bit of the drill string.

A power analysis can be performed to determine the amount or type ofrock interacting with the plasma. The amount of formation vaporized orcrushed can correlate to the amount of power supplied to the formationand the electrical characteristics of both the plasma and the formation.As the power supplied to the generate the plasma increases, the amountof formation material vaporized can expected to increase which cancorrelate to an increase in the exposed surface area of the formation orcuttings interacting with the plasma. Higher power pushes the reactionsto more complete products, such as hydrogen, carbon dioxide, and oxygen.Higher power may also increase halogen production, if halogens arepresent. As described above, the amount of rock interacting with theplasma can also be determined. Further, an arc to spark ratio can becorrelated to physical or electrical properties of the formation. Higherpower may equate to more arc than spark. For example, the arc to sparkratio can provide information about the formation such as breakdownvoltage, conductivity, resistivity, Young's modulus, shear modulus, bulkmodulus, Poisson's ratio, anisotropy, etc., especially if correlated todrilling rate. Plasma arc and plasma sparks generate different types offluid bubbles in the formation and consequently interact differentlywith the formation, particularly if the formation is anisotropic.Further, the chemical reactions mediated by plasma arc and plasma sparkreactions are differentiable based on the measured chemical reactionproducts and reaction rates, as described in reference to blocks 322,326 and/or 328 of FIG. 3B.

At block 604, the concentration of hydrocarbon chemical species in thecollected samples of downhole fluids is determined. For example, withreference to FIG. 1, the analysis system 160 can make thisdetermination. To determine the concentration of hydrocarbon chemicalspecies present in the collected samples of downhole fluids, theanalysis system 160 can perform operations to classify the organicchemical species present in the fluid samples through chemical analysis.The chemical analysis performed may be substantially similar to theanalysis described in FIGS. 3A-3B. Organic chemical species can includehydrocarbons and other organic chemicals that may be downhole such asoxygen and hydroxyl containing compounds, nitrogen-containing compounds,phosphorus-containing compounds, etc. Chemical species that do notcontain carbon, and are therefore not organic chemical species, may alsobe analyzed together with the hydrocarbon chemical species. The range ofspecies analyzed can depend on the system selected for analysis (i.e.gas chromatograph, mass spectrometer, or any of the instrumentationdescribed in reference to FIG. 1) and on the filtration system used toprepare the sample for analysis and protect the equipment. The analysissystem 160 may be protected from inorganic, corrosive, caustic, or otherreactive species by a pre-filter or column, such as one that removespolar substances and molecules from the analysis stream. In someembodiments, a polar substance is a chemical species in which thedistribution of electrons between the covalently bonded atoms is noteven. The analysis system 160 analyzes the collected fluid samples todetermine the presence of organic or nonpolar matter, such ashydrocarbons. The analysis system 160 can determine the presence ofnonpolar gasses, such as hydrogen, carbon dioxide, etc., or such gassesmay be separated from the fluid stream before analysis, such as by aphase separation membrane.

At block 606, a concentration of volatile inorganic chemical species(VICSs) in the collected sample is determined. For example, withreference to FIG. 1, the analysis system 160 can make thisdetermination. VICSs can be inorganic chemical species that have highvapor pressure at standard temperatures and pressures. Volatilesubstances more readily condense or vaporize than non-volatilesubstances. In downhole application, VICSs can include halogens or otherelements that may have become volatized. While the analysis describedbelow is described with respect to inorganic chemical species, it mayalso be applied to VICS and polar chemical species. The analysis system160 can analyze the formational and non-formational fluids in the sampleat the surface or, alternately, at a location between the drill bit andthe surface. The concentration of VICSs in the collected sample can bemeasured, and the concentration of the atoms, including trace elements,from the formation that were volatilized can be calculated from themeasured concentration and based on reaction stoichiometry and reactionrates. The hydrocarbon reaction rates, such as those calculated in block326 of FIG. 3B can be further correlated to constituents of theformation which act as catalysts or retardants of the previouslydetermined reactions (such as those described by Equation 28).

The analysis system 160 can analyze the collected fluid samples todetermine the presence of inorganic or polar matter. Common inorganicmatter present in the formation that may impact chemical reactionsinclude silica, carbon dioxide, silver, sulfur, and/or other impuritiesand trace elements incorporated within the formation rock or sediment.When the formation interacts with the plasma, side products can beproduced in addition to the products in Equation 28. Plasma reactionscan vaporize portions of the formation rock, in addition to formationfluid. For example, rocks that make up formation support structures cancontain reactive and catalytic atoms in trace or substantial amounts.Such atoms, including halogen atoms, heavy metals atoms, etc., cancontribute to the chemical reactions occurring as a result of the plasmageneration—either as catalysts or as reactants.

Halogen-containing compounds and other volatile compounds are commonside products of formation interaction: both organohalides(organochlorides, organobromides, etc.) and halogen gas (chlorine,bromine, etc.) can be produced. Such products can be inorganic (forexample chlorine gas) or can be organic but polar (such as theorganochloride chloroform)—neither of which are nonpolar hydrocarbons.As such, both can be filtered out before gas chromatography as they canbe corrosive to chromatography columns. Other side products can formfrom trace metals in the formation, such as platinum, iron, manganese,etc.

The analysis system 160 can analyze the collected fluid samples todetect the presence of any side products related to the presence ofnon-hydrocarbon matter. One way to determine the presence ofnon-hydrocarbon material is through the detection of abnormal,unexpected, or odd masses in the stoichiometry of the chemicalreactions, where masses of hydrocarbons are well known combinations ofthe atomic weights of multiples of hydrogen and carbon atoms as shown inEquation 48:Molecular Weight=m*1.008+n*12.011  (48)where n is the number of carbon atoms in the hydrocarbon molecule and mis the number of hydrogen atoms in the hydrocarbon molecule. Further,the relationship between m and n is defined for each type ofhydrocarbon, as shown in Table 2, below. By substituting the number ofhydrogen atoms (m) into Equation 48 for each type of hydrocarbon, themolecular weight as a function of the number of carbons (n) can becalculated (as shown in Table 2).

TABLE 2 Example Hydrocarbon Molecular Weights Type of Hydrocarbon Numberof Hydrogen Atoms Molecular Weight (Da) Alkane m = 2n + 2 n * 14.027 +2.016 Naphthene m = 2n + 2 − r n * 14.027 − r * 1.008 Alkene m = 2n n *14.027 Alkyne m = 2n − 2 n * 14.027 − 2.016 Polyunsaturated m = 2n + 2 −2d n * 14.027 + 2.016 − 2.016 * d

For alkanes, there are 2n+2 hydrogen atoms for n carbon atoms. Fornaphthenes, there are 2n+2−r hydrogen atoms for each n carbon atoms,where r represents the number of rings in each naphthene molecule. Foralkenes, there are 2n hydrogen atoms for each n carbon atoms. Foralkynes, there are 2n−2 hydrogen atoms for each n carbon atoms. Assaturation decreases, one or more carbon-carbon double or triple bondscan be formed, and the number of hydrogens for each carbon atom candecrease. Each additional higher order bond (i.e. each π bond) cancorrespond to the removal of two carbon orbital (one from each carbonatom) previously bonded to hydrogen atoms, as the two carbon atomsinvolved in the higher order bonds switch from sp^(a) hybridization tosp² hybridization or from sp² hybridization to sp hybridization.Therefore, poly-unsaturated hydrocarbons have the general formC_(n)H_(m) where m=2n+1−2d where d represents the number of π bonds inthe molecule (d is related to but not identical with the degree ofunsaturation). This gives a generalized hydrocarbon atomic weight of14.027*n+2.016−2.016*d, which, when rounded, tends to be an evenmolecular weight. Molecules that do not have a molecular weight in thisgeneral form can be identified as corresponding to molecules other thanhydrocarbons.

Abnormal molecular masses may be masses of odd numbers, as hydrocarbonchemical reactions typically produce molecules with molecular masseswith even numbers, as explained above. A spectrometer or gaschromatography-mass spectrometer may analyze the collected samples todetect the abnormal masses—i.e. masses that do not correspond tohydrocarbons—or may analyze all constituents and selectively identifymasses not corresponding to saturated or poly-unsaturated hydrocarbonmolecules. Table 3 shows example atoms together with their mass numberand naturally occurring isotopic concentration, plus the average atomicmass in Daltons (Da) and Pauling electronegativity in electron Volts(eV) for each element.

TABLE 3 Atomic Weight and Isotopic Concentration for Example ConstituentAtoms Atomic Pauling Abbre- Mass In Mass Electronegativity Elementviation Number Nature (Da) (eV) Hydrogen H 1 99.98%  1.008 2.20Deuterium D or ²H 2 0.02% Carbon C 12 98.93%  12.011 2.55 13-Carbon ¹³C13 1.07% 16-Oxygen O 16 99.76%  15.999 3.44 17-Oxygen ¹⁷O 17 0.04%18-Oxygen ¹⁸O 18 0.20% Fluorine F 19 ~100%  18.998 3.98 35-Chlorine ³⁵Cl35  76% 35.45 3.16 37-Chlorine ³⁷Cl 37  24% 79-Bromine ⁷⁹Br 79  51%79.904 2.96 81-Bromine ⁸¹Br 81  49% Iodine I 127 ~100%  126.90 2.66Manganese ⁵⁵Mn 55 ~100%  54.938 1.55 Platinum ¹⁹⁵Pt 195 33.83%  195.082.28

The analysis system 160 can determine one or more concentrations forchemical reaction product species based on mass spectrometry results.The presence of polar molecules, organohalides, metal complexes, etc.,in the mass spectrograph can be correlated directly to the presence ofoxygen, halogen, and metallic atoms in the formation and formationfluid, where such atoms act as reactants during the chemical reactionproduced by the plasma. Several example reactions are shown below inEquations 49-52:H₂C═CH₂+HCl→CH₃CH₂Cl  (49)4HCl+O₂→2Cl₂+2H₂O  (50)FeAsS+3O₂→AsO₃+SO₂+Fe_(x)O_(y)  (51)Fe(CO)₅+2C₅H₆→Fe(C₅H₆)₂+5CO+H₂  (52)Equations 49-52 are representative of possible reactions that can occurbetween the chemical constituents of the formation and are mediated bythe plasma. Individual atoms and molecules, including inorganic speciessuch as chlorine gas, iron oxide, etc. can also be produced.Non-hydrocarbon side products can be formed directly from hydrocarbonand formation interactions, or from the interaction of reaction products(such as those shown in Equation 28) with the formation, or reactionproducts (e.g. carbon dioxide, oxygen, hydrogen) generated in one plasmaevent acting on the formation in a subsequent plasma event. Individualatoms, such as metals like platinum may also be found in their nativestates (i.e. Pt) or in oxides (such as MnO₂). The concentration ofnon-hydrocarbon constituents in the drilling fluid can range fromsignificant percentages (water up to 10%, for example) to trace amounts(such as manganese which is found in soils in ranges of 7-9000 parts permillion (ppm) and may enter drilling fluid in orders of magnitudesmaller quantities).

Elements can be further determined from mass spectrometry based on theirisotopic concentrations. Mass spectrometry measures a mass-to-chargeratio, where isotopes of a single element appear as neighboring peakswith heights or intensities proportional to their relative abundance.These peaks may be small satellite peaks, as for carbon where ¹³C isapproximately 1.1% of all naturally occurring carbon, or these peaks maybe of the same order of magnitude, as for bromine, where approximately51% of naturally occurring bromine is ⁷⁹Br and 49% is ⁸¹Br. Thedistinctive relationship between isotopes of each element can contributeto a determination of the atomic makeup of the molecules detected bymass spectrometry. The effect of isotope can be cumulative—i.e. eachatom in a molecule can be an isotope, which can lead to a smearing ofmass peaks for one molecule. For example, for hexane (molecular formulaC₆H₁₂), the ¹²C and ¹H peak at 86 Da is 93.49% (i.e. 0.9893⁶*0.9998¹⁴)of the total detected hexane, while the peak at 87 Da is 6.33% (i.e.6*0.0107*0.9893⁵*0.9998¹⁴+14*0.0002*0.9893⁶*0.9998¹³) of the totaldetected hexane, when carbon and hydrogen isotopes are assumed to occurat their natural abundance. These two percentages do not sum to unity,because the small percentage of hexane molecules that contain two ormore isotopes also contribute to the whole. The relationship betweencarbon isotopes gives rise to the general Equation 53:

$\begin{matrix}{n = \frac{100Y}{1.1X}} & (53)\end{matrix}$where n is the number of carbon atoms, X is the amplitude of the ionpeak at a molecular weight to charge M, and Y is the amplitude of theion peak at a molecular weight to charge M+1. The relationships betweenpeaks can, therefore, provide information about the atoms that make upthe molecule to which the peak corresponds.FIG. 7 depicts an example mass spectrometry graph, according to one ormore embodiments. FIG. 7 depicts a mass spectrometry graph 700. Thegraph 700 represents an example output of quadrupole analog massspectrometry. The graph 700 has an x-axis 701 of mass to charge ratio(mass/charge) in units of kilogram (kg)/Coulomb (C). The graph 700 has ay-axis 702 representing intensity. A line 703 represents the massspectrum of a sample. The line 703 may have peaks 704-712. Each peak704-712 represents an ion having a specific mass to charge ratio. Thearea under the peak indicates the concentration of the ion. Peaks 704,710, 711, and 712 are single peaks most likely representing a singleion. Peaks 705, 706, and 707 and peaks 708 and 709 are clustered.Clusters of peaks may represent spectral fingerprints or satellitepeaks. The cluster of peaks 705, 706, and 707 most likely represent aspectral fingerprint of water. The cluster of peaks 708 and 709 mostlikely represent a satellite peak of silicon.

Returning to FIG. 6 at block 608, the determined VICSs are equated topossible formation types based on mineral composition of the formation.For example, with reference to FIG. 1, the computer 162 can perform thisequating of VICSs to possible formation types. Different formation typescan be composed of rocks of various minerals. Minerals can be determinedbased on the combination of VICSs determined in the inorganic analysis.For example, some combinations of aluminum oxides and other chemicalconstituents may indicate the presence of chlorites, which may beindicative of igneous or metamorphic rock, while other combinations ofaluminum oxides and different chemical constituents may be indicative ofillite, which may be indicative of a sedimentary rock formation.

To illustrate, table 4 is an example of a table for classifyingformation type based on volatile inorganic chemical species, accordingto one or more embodiments. Table 4 lists common minerals often found inrock formations and the some of the VICSs that may be indicative of themineral's presence in the formation. Table 4 is provided for examplepurposes only, as tables used for classifying formation type may containhundreds of possible minerals and combinations of VICSs. A sample ofcommon minerals found in oil and gas producing formations are providedin table 4. From table 4, it can be seen that many minerals are composedof similar VICSs, but each mineral has a unique combination of VICSs.For example, silicon dioxide (SiO₂) is present in chlorite, albite,illite, kaolinite, and quartz. If the silicon dioxide is one of thedetermined VICSs, the computer 162 would select only those elements aspossible minerals. If aluminum oxide (Al₂O₃) was also a determined VICS,the computer could eliminate quartz as a possible mineral type as quartzcontains no aluminum oxide. This process can continue until all VICSs inthe formation are detected or until one or more mineral types aredetermined.

Based on the detected VICSs, the computer 162 can determine possibleminerals which correlate to formation types. For example, barite occursis sedimentary formations such as limestone rock while dolomite occursin sedimentary carbonate formations. The computer 162 may selectpossible types, eliminate possible types, or perform a combination ofboth. For selecting possible formation types, the computer 162 cancompare the determined VICSs to the known chemical constituents ofdifferent formation types and select the formation types which containthe determined VICSs. When eliminating possible formation types, thecomputer 162 cannot consider any possible formation type that does notinclude the determined VICSs, thereby leaving behind only formationtypes which contain the determined VICSs as possible formation types.

TABLE 4 Formation Classification based on VICSs Composition of Mineralsin Rock Mineral Volatile Inorganic Chemical Species Rutile TiO₂ TiO₂Fluorapatite Ca₅(PO₄)₃(F) P₂O₅ CaO Barite BaSO₄ BaO SO₃ Pyrite FeS₂ SO₃Chlorite Mg₃Fe₃Si₂Al₂•O₁₀(OH)₈ Fe₂O₃ MgO Al₂O₃ SiO₂ (Mg, Fe)₃(Si,Al)₄O₁₀ Mg_(1.5)Fe_(1.5)Si₂Al₂O₁₀• (OH)₂•(Mg, Fe)₂(OH)₆(OH)₂Mg_(1.5)Fe_(1.5)•(OH)₆ Dolomite Ca_(0.5)Mg_(0.5)CO₃ MgO CaO CalciteCaCO₃ CaO Halite NaCl Cl Na₂O Albite NaAlSi₃O₈ Na₂O Al₂O₃ SiO₂(Naplagioclase) Illite KAl₄(Si₇AlO₂₀)•(OH)₄ K₂O Al₂O₃ SiO₂ —K_(1.5-1.0)Al₄•(Si_(6.5-7.0)Al_(1.0-1.5)O₂₀)(OH)₄ KaoliniteA1₂Si₂O₅(OH)₄ Al₂O₃ SiO₂ Quartz SiO₂ SiO₂

At block 610, the generalized chemical equation for plasma reactions,such as Equation 28, is adjusted for changes due to the formation type.For example, with reference to FIG. 1, the computer 162 can make thisadjustment. During plasma reactions with fluid, energy is absorbed bythe formation. The conductivity of the formation itself can beindependent of the formation fluid in the pore spaces (the conductivityof the formation together with the formational fluid is dependent uponthe formational fluid conductivity and the permeability orinterconnectedness of the fluid-filled pores). Loss of energy to theformation, similar to loss of energy or current to ground, reduces theenergy available for chemical reactions, independent of the fluidcharacteristics. The reduction in energy for plasma-based chemistryshifts the possible chemical reactions because less energy is availableto produce the molecular kinetic energy necessary to react transitionstates (i.e. activation energy E_(a)) or the energy necessary to produceproducts (i.e. enthalpy of formation). This can be identified in theresultant products. The shift can be exhibited in two forms: theformational compounds may catalyze the reaction, or the aqueous ororganic liquid phase reactions may shift due to the introduction ofreactants from the formation. These shifts are incorporated into thegeneralized chemical equation for plasma reactions to represent thedownhole environment more accurately.

At block 612, the power loss to the formation is determined. Forexample, with reference to FIG. 1, the analysis system 160 can make thisdetermination. Similar methods and equations to those described in block306 of FIG. 3A may be used to determine the power loss to the formation.Determining the power loss may also be experimentally determined.Experimentally determining the power loss may include calculating apower loss based on equations, such as those described in FIG. 3A, or itmay include monitoring the power downhole for changes.

At block 614, the power loss is equated to the possible formation types,as determined in block 608. For example, with reference to FIG. 1, thecomputer 162 can make this equaling of power loss to possible formationtypes. Conductivity is a measure of how easily electric current can flowthrough a given material. Conductivity represents a power loss within amaterial. The conductivities of different rock types are known values.Conductivities of a specific rock type may span many orders of magnitudedepending on porosity, permeability, connectivity, temperature, degreeof fluid saturation, etc. of the formation. For example, granite-bearingrocks are highly conductive while carbonate rocks and unconsolidatedsediments are very resistive. By comparing the possible formation types,determined at block 608, to the power loss to the formation, thecomputer 162 can further limit possible rock and formation types. Thecomputer 162 can compare the power loss values to the ranges ofconductivities for each of the determined possible formation types.Power loss values falling within the known ranges for each rock andformation type indicate a possible match, and thus a viable rock andformation option. These options are selected, or maintained, as possibleformation types. Power loss values outside a range of conductivityvalues for one of the determined possible formation types indicate therock and formation type are not a match, and thus, the rock andformation type are not a viable option for the drilled formation. Theserock and formation types can be removed from further analysis.

At block 616, the possible formation types are constrained based onsolid composition analysis. For example, with reference to FIG. 1, thecomputer 162 can perform this constraining. The computer 162 may performsolid composition analysis to analyze physical samples collected fromthe downhole environment. Solid composition analysis may includeoperations for monitoring cuttings as described in block 310 of FIG. 3B.Solid composition analysis may also include analysis using techniquesrelated to inductively coupled plasma mass spectroscopy (ICP-MS), x-raypowder diffraction (XRD), and/or x-ray fluorescence (XRF). For example,with reference to FIG. 1, the instrumentation 161 may perform thismeasurement and the computer 162 may perform the analysis. Solidcomposition analysis can provide another means of narrowing down thepossible formation types. The solid composition analysis can provide atleast some of the rock types contained in the formation. Based on thesolid composition analysis, the computer 162 can eliminate any remainingformation types that do not contain the rocks identified in the solidcomposition analysis. There may be one or more rock and/or formationtypes remaining as possible formation types. This is possible becausedrilling may occur through many formation layers, and individualformation layers may contain various rock types.

At block 618, the formation type is determined. For example, withreference to FIG. 1, the computer 162 can make this determination basedon operations at block 614 (and possibly operations at block 616). Thedetermined formation type can be one or multiple types.

The flowcharts are provided to aid in understanding the illustrationsand are not to be used to limit scope of the claims. The flowchartsdepict example operations that can vary within the scope of the claims.Additional operations may be performed; fewer operations may beperformed; the operations may be performed in parallel; and theoperations may be performed in a different order. It will be understoodthat each block of the flowchart illustrations and/or block diagrams,and combinations of blocks in the flowchart illustrations and/or blockdiagrams, can be implemented by program code. The program code may beprovided to a processor of a general-purpose computer, special purposecomputer, or other programmable machine or apparatus.

As will be appreciated, aspects of the disclosure may be embodied as asystem, method or program code/instructions stored in one or moremachine-readable media. Accordingly, aspects may take the form ofhardware, software (including firmware, resident software, micro-code,etc.), or a combination of software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”The functionality presented as individual modules/units in the exampleillustrations can be organized differently in accordance with any one ofplatform (operating system and/or hardware), application ecosystem,interfaces, programmer preferences, programming language, administratorpreferences, etc.

Any combination of one or more machine readable medium(s) may beutilized. The machine-readable medium may be a machine-readable signalmedium or a machine-readable storage medium. A machine readable storagemedium may be, for example, but not limited to, a system, apparatus, ordevice, that employs any one of or combination of electronic, magnetic,optical, electromagnetic, infrared, or semiconductor technology to storeprogram code. More specific examples (a non-exhaustive list) of themachine readable storage medium would include the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a portable compact disc read-only memory (CD-ROM), anoptical storage device, a magnetic storage device, or any suitablecombination of the foregoing. In the context of this document, amachine-readable storage medium may be any tangible medium that cancontain or store a program for use by or in connection with aninstruction execution system, apparatus, or device. A machine-readablestorage medium is not a machine-readable signal medium.

A machine-readable signal medium may include a propagated data signalwith machine readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Amachine readable signal medium may be any machine readable medium thatis not a machine readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a machine-readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

The program code/instructions may also be stored in a machine readablemedium that can direct a machine to function in a particular manner,such that the instructions stored in the machine readable medium producean article of manufacture including instructions which implement thefunction/act specified in the flowchart and/or block diagram block orblocks.

Example Computer

FIG. 8 depicts an example computer, according to one or moreembodiments. The computer includes a processor 801 (possibly includingmultiple processors, multiple cores, multiple nodes, and/or implementingmulti-threading, etc.). The computer includes a memory 807. The memory807 may be system memory or any one or more of the above alreadydescribed possible realizations of machine-readable media. The computeralso includes a bus 803 and a network interface 805. The computer alsoincludes an organic analyzer 811, an inorganic analyzer 813, and an arcand spark analyzer 815. Any one of the previously describedfunctionalities may be partially (or entirely) implemented in hardwareand/or on the processor 801. For example, the functionality may beimplemented with an application specific integrated circuit, in logicimplemented in the processor 801, in a co-processor on a peripheraldevice or card, etc. Further, realizations may include fewer oradditional components not illustrated in FIG. 8 (e.g., video cards,audio cards, additional network interfaces, peripheral devices, etc.).The processor 801 and the network interface 805 are coupled to the bus803. Although illustrated as being coupled to the bus 803, the memory807 may be coupled to the processor 801.

While the aspects of the disclosure are described with reference tovarious implementations and exploitations, it will be understood thatthese aspects are illustrative and that the scope of the claims is notlimited to them. In general, techniques for determining rock type basedon plasma chemistry as described herein may be implemented withfacilities consistent with any hardware system or hardware systems. Manyvariations, modifications, additions, and improvements are possible.

Plural instances may be provided for components, operations orstructures described herein as a single instance. Finally, boundariesbetween various components, operations and data stores are somewhatarbitrary, and particular operations are illustrated in the context ofspecific illustrative configurations. Other allocations of functionalityare envisioned and may fall within the scope of the disclosure. Ingeneral, structures and functionality presented as separate componentsin the example configurations may be implemented as a combined structureor component. Similarly, structures and functionality presented as asingle component may be implemented as separate components. These andother variations, modifications, additions, and improvements may fallwithin the scope of the disclosure.

Use of the phrase “at least one of” preceding a list with theconjunction “and” should not be treated as an exclusive list and shouldnot be construed as a list of categories with one item from eachcategory, unless specifically stated otherwise. A clause that recites“at least one of A, B, and C” can be infringed with only one of thelisted items, multiple of the listed items, and one or more of the itemsin the list and another item not listed.

Example Embodiments

Example embodiments include the following:

Embodiment 1: A method comprising: determining chemical species releasedinto a drilling fluid after a rock of a subsurface formation hasinteracted with a plasma discharge produced via one or more electrodesof a drill bit of a pulse power drill string disposed in a borehole fordrilling the borehole in the subsurface formation; correlating thechemical species to an attribute of the subsurface formation thatinteracted with the plasma discharge; and classifying a type of the rockof the subsurface formation that interacted with the plasma dischargebased on the correlating.

Embodiment 2: The method of embodiment 1, wherein the attribute of thesubsurface formation comprises a conductivity.

Embodiment 3: The method of embodiment 2, wherein the correlatingcomprises comparing a power loss to the formation after the rock of thesubsurface formation has interacted with the produced plasma dischargeto the conductivity.

Embodiment 4: The method of embodiments 1, 2, or 3, wherein determiningthe chemical species released into a drilling fluid after a rock of asubsurface formation has interacted with a plasma discharge comprises:determining concentrations of inorganic chemical species released intothe drilling fluid; and determining possible types of rock of thesubsurface formation based on the determined concentrations of inorganicchemical species.

Embodiment 5: The method of embodiments 1, 2, 3, or 4, wherein theinteraction between the rock and the plasma discharge releases volatileinorganic chemical species related to the rock type into the drillingfluid.

Embodiment 6: The method of embodiments 1, 2, 3, 4, or 5, furthercomprising: determining organic chemical species released into thedrilling fluid.

Embodiment 7: The method of embodiments 1, 2, 3, 4, 5, or 6, furthercomprising classifying a type of the rock of the subsurface formationthat interacted with the plasma discharge based on an analysis of solidmaterial from the drilled subsurface formation.

Embodiment 8: A non-transitory, computer-readable medium havinginstructions stored thereon that are executable by a computing device toperform operations comprising: determining chemical species releasedinto a drilling fluid after a rock of a subsurface formation hasinteracted with a plasma discharge produced via one or more electrodesof a drill bit of a pulse power drill string disposed in a borehole fordrilling the borehole in the subsurface formation; correlating thechemical species to an attribute of the subsurface formation thatinteracted with the plasma discharge; and classifying a type of the rockof the subsurface formation that interacted with the plasma dischargebased on the correlating.

Embodiment 9: The non-transitory, computer-readable medium of embodiment8, wherein the attribute of the subsurface formation comprises aconductivity.

Embodiment 10: The non-transitory, computer-readable medium ofembodiment 9, wherein correlating the chemical species to an attributeof the subsurface formation that interacted with the plasma dischargecomprises comparing a power loss to the formation after the rock of thesubsurface formation has interacted with the produced plasma dischargeto the conductivity.

Embodiment 11: The non-transitory, computer-readable medium ofembodiment 8,9, or 10, wherein determining the chemical species releasedinto a drilling fluid after a rock of a subsurface formation hasinteracted with a plasma discharge comprises: determining inorganicchemical species released into the drilling fluid; and determiningpossible types of rock of the subsurface formation based on thedetermined inorganic chemical species.

Embodiment 12: The non-transitory, computer-readable medium ofembodiment 8, 9, 10, or 11, wherein the interaction between the rock andthe plasma discharge releases volatile inorganic chemical speciesrelated to the rock type into the drilling fluid.

Embodiment 13: The non-transitory, computer-readable medium ofembodiment 8, 9, 10, 11, or 12 wherein the operations further comprise:determining organic chemical species released into the drilling fluid.

Embodiment 14: The non-transitory, computer-readable medium ofembodiment 8, 9, 10, 11, 12, or 13, wherein the operations furthercomprise classifying a type of the rock of the subsurface formation thatinteracted with the plasma discharge based on an analysis of solidmaterial from the drilled subsurface formation.

Embodiment 15: A system comprising: a pulse power drill stringconfigured to be positioned in a borehole formed in a subsurfaceformation, wherein the pulse power drill string comprises a drill bitwith one or more electrodes to periodically emit an electrical dischargeto drill the borehole; a sample extractor configured to collect a sampleof drilling fluid that circulated down the borehole after the drillingfluid has interacted with the electrical discharge; a processor; and acomputer-readable medium having instructions stored thereon that areexecutable by the processor to cause the system to, determine chemicalspecies released into the drilling fluid after a rock of the subsurfaceformation has interacted with the electrical discharge, correlate thechemical species to an attribute of the subsurface formation thatinteracted with the electrical discharge, and classify a type of therock of the subsurface formation that interacted with the electricaldischarge based on the correlating.

Embodiment 16: The system of embodiment 15, wherein the attribute of thesubsurface formation comprises a conductivity.

Embodiment 17: The system of embodiment 16, wherein the instructionsexecutable by the processor to cause the system to correlate compriseinstructions executable by the processor to cause the system to comparea power loss to the formation after the rock of the subsurface formationhas interacted with the produced plasma discharge to the conductivity.

Embodiment 18: The system of embodiment 15, 16, or 17, wherein theinstructions executable by the processor to cause the system todetermine the chemical species released into a drilling fluid after arock of a subsurface formation has interacted with the electricaldischarge comprise instructions executable by the processor to cause thesystem to: determine inorganic chemical species released into thedrilling fluid; and determine possible types of rock of the subsurfaceformation based on the determined inorganic chemical species.

Embodiment 19: The system of embodiment 15, 16, 17, or 18, wherein theinstructions further comprise instructions executable by the processorto cause the system to: determine organic chemical species released intothe drilling fluid.

Embodiment 20: The system of embodiment 15, 16, 17, 18, or 19, whereinthe instructions further comprise instructions executable by theprocessor to cause the system to: classify a type of the rock of thesubsurface formation that interacted with the plasma discharge based onan analysis of solid material from the drilled subsurface formation.

As used herein, the term “or” is inclusive unless otherwise explicitlynoted. Thus, the phrase “at least one of A, B, or C” is satisfied by anyelement from the set {A, B, C} or any combination thereof, includingmultiples of any element.

The invention claimed is:
 1. A method comprising: determining thepresence of one or more chemical species released into a drilling fluidas a result of a rock of a subsurface formation having interacted with aplasma discharge produced via one or more electrodes of a drill bit of apulse power drill string disposed in a borehole for drilling theborehole in the subsurface formation; correlating the presence of theone or more chemical species released into the drilling fluid after therock of the subsurface formation has interacted with the plasmadischarge to an attribute of the subsurface formation; and classifying atype of the rock of the subsurface formation that interacted with theplasma discharge based on the correlating.
 2. The method of claim 1,wherein the attribute of the subsurface formation comprises aconductivity.
 3. The method of claim 2, wherein the correlatingcomprises comparing a power loss to the formation after the rock of thesubsurface formation has interacted with the produced plasma dischargeto the conductivity.
 4. The method of claim 1, wherein determining thepresence of one or more chemical species released into a drilling fluidas the result of the rock of the subsurface formation having interactedwith the plasma discharge comprises: determining concentrations of oneor more inorganic chemical species released into the drilling fluid; anddetermining possible types of rock of the subsurface formation based onthe determined concentrations of the one or more inorganic chemicalspecies.
 5. The method of claim 1, wherein the interaction between therock and the plasma discharge releases one or more volatile inorganicchemical species related to the rock type into the drilling fluid. 6.The method of claim 1, further comprising: determining the presence ofone or more organic chemical species released into the drilling fluid.7. The method of claim 1, further comprising classifying a type of therock of the subsurface formation that interacted with the plasmadischarge based on an analysis of solid material from the drilledsubsurface formation.
 8. A non-transitory, computer-readable mediumhaving instructions stored thereon that are executable by a computingdevice to perform operations comprising: determining the presence of oneor more chemical species released into a drilling fluid as a result of arock of a subsurface formation having interacted with a plasma dischargeproduced via one or more electrodes of a drill bit of a pulse powerdrill string disposed in a borehole for drilling the borehole in thesubsurface formation; correlating the presence of the one or morechemical species released into the drilling fluid after the rock of thesubsurface formation has interacted with the plasma discharge to anattribute of the subsurface formation; and classifying a type of therock of the subsurface formation that interacted with the plasmadischarge based on the correlating.
 9. The non-transitory,computer-readable medium of claim 8, wherein the attribute of thesubsurface formation comprises a conductivity.
 10. The non-transitory,computer-readable medium of claim 9, wherein correlating the presence ofthe one or more chemical species to an attribute of the subsurfaceformation that interacted with the plasma discharge comprises comparinga power loss to the formation after the rock of the subsurface formationhas interacted with the produced plasma discharge to the conductivity.11. The non-transitory, computer-readable medium of claim 8, whereindetermining the presence of the one or more chemical species releasedinto a drilling fluid as the result of the rock of a subsurfaceformation having interacted with the plasma discharge comprises:determining the presence of one or more inorganic chemical speciesreleased into the drilling fluid; and determining possible types of rockof the subsurface formation based on the determined presence of the oneor more inorganic chemical species.
 12. The non-transitory,computer-readable medium of claim 8, wherein the interaction between therock and the plasma discharge releases one or more volatile inorganicchemical species related to the rock type into the drilling fluid. 13.The non-transitory, computer-readable medium of claim 8, wherein theoperations further comprise: determining the presence of one or moreorganic chemical species released into the drilling fluid.
 14. Thenon-transitory, computer-readable medium of claim 8, wherein theoperations further comprise classifying a type of the rock of thesubsurface formation that interacted with the plasma discharge based onan analysis of solid material from the drilled subsurface formation. 15.A system comprising: a pulse power drill string configured to bepositioned in a borehole formed in a subsurface formation, wherein thepulse power drill string comprises a drill bit with one or moreelectrodes to periodically emit an electrical discharge to drill theborehole; a sample extractor configured to collect a sample of drillingfluid that circulated down the borehole after the drilling fluid hasinteracted with the electrical discharge; a processor; and acomputer-readable medium having instructions stored thereon that areexecutable by the processor to cause the system to, determine thepresence of one or more chemical species released into the drillingfluid as a result of a rock of the subsurface formation havinginteracted with the electrical discharge, correlate the one or morechemical species released into the drilling fluid after the rock of thesubsurface formation has interacted with the electrical discharge to anattribute of the subsurface formation, and classify a type of the rockof the subsurface formation that interacted with the electricaldischarge based on the correlating.
 16. The system of claim 15, whereinthe attribute of the subsurface formation comprises a conductivity. 17.The system of claim 16, wherein the instructions executable by theprocessor to cause the system to correlate comprise instructionsexecutable by the processor to cause the system to compare a power lossto the formation after the rock of the subsurface formation hasinteracted with the produced plasma discharge to the conductivity. 18.The system of claim 15, wherein the instructions executable by theprocessor to cause the system to determine the presence of the one ormore chemical species released into the drilling fluid after the rock ofthe subsurface formation has interacted with the electrical dischargecomprise instructions executable by the processor to cause the systemto: determine the presence of one or more inorganic chemical speciesreleased into the drilling fluid; and determine possible types of rockof the subsurface formation based on the determined presence of the oneor more inorganic chemical species.
 19. The system of claim 15, whereinthe instructions further comprise instructions executable by theprocessor to cause the system to: determine the presence of one or moreorganic chemical species released into the drilling fluid.
 20. Thesystem of claim 15, wherein the instructions further compriseinstructions executable by the processor to cause the system to:classify a type of the rock of the subsurface formation that interactedwith the plasma discharge based on an analysis of solid material fromthe drilled subsurface formation.